My recommendation for the world tour is
1. a frame-mounted ring lock (Abus, Basta) on each wheel
Plus
2. a lock that makes the bike unridable by unlocking the handlebar from the front wheel, like the n'Lock
http://shop.nlock.ch/Plus
3. a cable for tying the bike to something (the N'Lock comes with a mickey mouse cable; that's not what I mean!) -- the best cable that is still convenient locks into the ring lock and loops through other components and around fixed objects and releases at the same time as the ring lock
4. Pitlocks for the seat post and saddle, locks for luggage.
All of this should cost about a couple of hundred pounds but doesn't necessarily obviate the need for insurance (which covers your bike not only against theft but against accidents and fire, etc).
I don't find it difficult to fit an Abus D-lock; like everyone else who's ever handled one, I swear by the Abus Granite X-plus 54, and use mine every time I leave the house. It depends on which of the many available clips you have. Mine has the one-handed clip for the down tube attached just under the seat at an angle so that clears the rack and pannier baskets, where it also falls conveniently to hand if a Range Rover comes too near me.
You can get ring locks, the good ones being made by Basta and Abus, for both the rear and front wheels, the rear wheel one is more common, more easily fitted and more convincing as engineering (there is no reason you shouldn't fit a rear ring lock at the front, if your bike is otherwise suited, which probably means disc brakes). The front design is different, and not so convincing. Ringlocks are in fact quite light, as only the ring needs to be sturdy at all, and the sheath can be any old flimsy rubbish, because once the ring is locked on, one of the bike's triangles needs to be broken to get it off, and the rim to be cut; there's no space for leverage. Many of these ring locks sold at retail are in fact OEM packages, so make sure you get the fitting kit as well.
The ring lock and n-Lock combination have the advantage that when they are open, not locked on, the keys sit in them.
So, with this combination, you have a bike that is visibly not suitable for use (the handlebars are at an obviously odd angle), so no riding away; no impulse crimes. The more professional thief doesn't want an inoperable bike; he moves on. If he has orders for your components, say a Rohloff box, he notes that the frame will have to be cut to get the wheel out, or all the spokes cut to get the box out. He moves on to a more cooperative target.
This little lot shouldn't add as much as two pounds to your bike, so you're ahead over the 3 pounds of the Abus Granite X-plus 54 which locks up only one wheel.
In fact, I might try the n'Lock myself now that they've reduced the prices.
Andre Jute