Hi Neil!
How exciting! A tour in the works; grand fun and Adventure await you and all best wishes in advance. You've a lovely machine to ride for it.
As for weight and distribution, a quick check of the RST portion of Thorn's Summer 2011 brochure reminds me of Andy Blance's recommended weight limits on page 8...
The RST can carry just 4kg on each side of its forks and will cope with 16kg at the back. This is its limit and the RST is not at its best near the limit!
A reasonable caution, given the more sporting nature and lighter tubing of the RST. A bit later in the page, Andy adds...
The RST is at its best with around 6kg, this load has no effect whatsoever on the bike's sublime handling. The RST will encourage you to keep trying harder as long as you don't overload it. I'd never want to travel far with more than 10kg on the back, unless the front was also carrying some weight.
Given these cautions, the amount of weight will help determine if you wish/need to carry front panniers.
You can surely tour on the RST; just keep the overall weight and its placement in check, and I think you'll do fine. You don't have to carry everything but the kitchen sink to have a good time or live in reasonable comfort while camping self-supported -- going the B&B route allows even more freedom. You'll do fine either way, I'm sure.
The matter of using front panniers or not is nearly as individual as the decision to wear a helmet, and there are people who are not only happy with their own way of doing things, but staunchly committed. In my own experience, I have found it helpful (necessary, from my perspective) to distribute the weight around the bike, so I use front panniers and sometimes a lightly loaded handlebar bag and heavily loaded rear panniers, but -- and this is key -- my frames are not as lightweight and sporting as an RST's. I had a Sherpa Mk2 (think: Raven Tour framewise) and now a Nomad M2, so weight and its placement was not as critical as on a lighter, more sporting machine. Reading AndyB's suggestions, it sounds as if front panniers are pretty necessary to maintain good handling if you approach the RST's weight limits.
Since you already have a full set of very nice bags (and tent!), I would suggest loading up the Super Cs in various configurations and giving them a try to see what works best for your needs on some test runs and day rides. This sort of "shakedown cruise" is tremendously valuable for finding what works for you, as are overnight "camping trips" in the backyard or very close to home. Those elements of the trip are little different from what you'll find on a RealTour™...and you are close enough to home to make changes quickly and easily without having to suffer much in the way of consequences if something doesn't work or fails. In this case, if riding with only a rear load "doesn't feel right", then you can spring for the front pannier racks. If things go well as-is, you can save the cash toward lodging or other things.
Given Andy B's counsel on weight, perhaps something light but bulky in the front bags would be just the thing -- a sleeping bag in one and your inflatable pad in the other, with a wind jacket and a fleece distributed in the remaining front bag space. That would free up more room in your rear bags/atop your rear rack, leave your most-used/changed clothing ready to hand, and keep within Andy B's endorsed weight limits on the forks.
As for daily distance and limits, I would suggest keeping the Danneaux's Fun Imperative
® in mind -- bike touring should be enjoyable on the face of it, so having realistic mileage goals helps a lot, especially early on if you're not used to doing it. Again -- I would suggest loading up the bags with the weight you expect to carry and doing some day rides in similar terrain (which may mean seeking out hills, slopes, and even loading ramps) to see how it goes. Low gearing will make any hill easier to conquer and add to the fun in doing so; you'll be carrying extra weight, after all, so don't hesitate to shift down when needed. "Tour" implies longer days in the saddle, and more consistent ones than the usual day-riding, so you may wish to adjust daily mileage downward a bit, adjust pace, and engineer in some rest days off the bike to stay fresher. Your 20-mile daily commutes will be a tremendous help, as you've already built a daily "base" on which to build your tour miles.
After some "engineered play", I think you'll know much better what your limits are, and where you will need to make changes.
Your planned trip sounds wonderful Neil and you're bound to have a good time. I can't wait to see photos on your return. Though my suggestions aren't specific, hopefully something will prove helpful going forward and you're almost guaranteed to receive helpful, on-target responses from other Forum members -- some of whom likely tour on RSTs.
Best,
Dan.
