All my bikes are set up the same to within one millimetre at the contact points of saddle, handgrips and pedals. No, the bike frames aren't precisely the same, but I've effectively made them the same by precise setup.
Before you even consider doing what I do, you should know I sit very upright, and I'm fanatical about ergonomic angles for knees, wrists and handgrips. I have no interest in deforming my body to cycle faster, so I don't use drops but North Road Bars, which are by far the most ergonomic bars you can get, regardless of the fact that some ergonomically wretched bars have "ergonomic" in their name. There's possibly a weight penalty to setting up the bike as a I do. My process works amazingly well on bikes from three manufacturers and of very different frame sizes though the angle-geometries are relatively close.
First of all, I set up the seat height so that the instep (not the ball of the foot as for proper athletic cycling) of my thick rubber-soled street shoes rest comfortably on the pedals with the knee just slightly crooked and the knee slightly in front of the instep-pedal position at the bottom of the stroke; if your legs are not the same length, you may have to compromise by setting seat height halfway between the correct positions for the two legs. The slightly bent knee at normal max stroke permits a modicum of extra power when necessary by very slightly going light over the saddle (rather than fully posting -- no daylight between my bum and the saddle will be visible). All this must be done with my back in the proper riding position, which is just slightly bent forward, say 15 degrees off the perfect vertical because perfectly vertical (right angles to the ground) would not only be uncomfortable and painful but could do your vertebrae permanent damage. Practically I start with the seat height right and the saddle tilted ever so slightly backwards or even perfectly horizontal. Then I slide the saddle forwards and backwards to position the knees over the pedals. There may need to be a further millimetre height adjustment of the seatpost to realign the knee over the instep if you're really finicky, and perhaps another millimetre of saddle adjustment as a consequence. When the adjustments are down to one millimetre, I generally call it near enough for my back.
So now two points are adjusted and I haven't yet added any weight to the bike, unless the frame is so undersize that an enormously long seatpost is required. The next step is trickier because we need to arrange two fixed points, the handgrips, in three dimensions with a given fixing point, the steering tube exposed length above the head tube, and available components, handlebars and stem, of fixed lengths and arcs.
Generally, since I sit so upright, the first three things I do is fit a long steering tube extender and fix it in the headset with a clamp lock of some kind (I use a seatpost clamp) so that it the bearings are correctly loaded without depending on the stem to hold everything together, stack spacers on top of that purely for cosmetic purposes, and fit an adjustable stem to the very top of the increased-length steering tube. Then I fit North Road bars, of which I have a selection with various rises though most often I use a cheap and common type Uno-Kalloy with a splay and downturn of the grips of which I approve. I rotate the whole handle bar inside the stem-clamp so the ends of the handlebar grips are about the level of the saddle nose or above it and fix it lightly in the handle-bar clamp of the stem. I loosen the stem's swivel clamp until it just holds the weight of the handlebar grip in place. Now I have a complete articulated steering assembly.
The next operation is to sit on the saddle in my preferred position with my feet on the pedals, and arrange the articulated steering assembly in three dimension to suit the length of my arms and the preferred angle of my wrists. Clearly everything must depend on one's reach with elbows slightly bent. So I grip the handlebars (which are fully assembled right down to the Brooks leather-ring grips I like, including controls and cables) which are splayed outwards at an angle that is natural to the tube through my fingers and thumbs enclosing the grips and turn the handlebars in the stem-clamp to point downwards at an angle that will straighten my wrists. I almost always use the Uno Kalloy 600-620mm wide North Road Bars, which make this process easy as the rise, grip splay and grip vertical angle are perfect for me. This usually brings the handlebar grips to above the saddle and quite a bit closer to the rider than is common today. It's a fair way from an old-fashioned gentleman's bicycling position, but it is equally far away from being on the drops too.
Troubleshooting. The entire handlebar pulls the adjustable stem in an arc, up and down, so there's usually no great problem caused by the desired ergonomic arrangement in three dimensions of control radius (arm length), straight wrists, and handhold splay and downturn. But if you can't satisfy all three at once, the first thing to look at is the position of the stem on the steering tube (or extension): you could move the stem down or get a longer steering tube extension (not so easy if you've already fitted the longest available). The next thing is to get a longer or shorter adjustable stem, but generally it shouldn't be necessary to go this far. Or you could get a handlebar with a different rise, but most of the ones available bring different geometric problems with them, and only the Uno-Kalloy comes with adequate length of handgrips: they're intended for you to saw bits off, but I have wide shoulders, plus a lot of controls I need under my thumb.
Now you can substitute a fixed stem of the correct length and angle, if you can find one, for the adjustable stem. I don't bother because the adjustable stem permanently on the bike allows me to make further adjustments as time goes by, and I am compulsive about forearm ergonomics because a writer is a sort of manual worker who operates a keyboard.
The key to giving yourself a proper bike fit -- rather than something some fellow thinks will suit a much more powerful athlete -- is the adjustable stem. You can do it with a solid stem, as when I fitted a non-adjustable n'lock, with the further complication of being closed on top so it has to fit at the very top of the steering tube, by having the correct length of steering extension tube, but it's a tricky conceptual and arithmetical problem not recommended for newbies, unless they actually like frustration.
It gets easier every time you do it, until I can now do it in less time than it takes to read this description of what I do.
