No plans to ride STP, being in the UK, but I'm a high mileage swift rider with some tips to share....

I would recommend trying drop bars for long mileage riding. I've been using flat bars and bull-bars for years and have struggled with back pain. I found bull bars great for most riding but the problem is that they don't give enough variety of riding position. I finally gave drop-bars a go a few weeks ago and my back has been much happier. You get 3 main positions (tops, drops and hoods) that are significantly different to each other for your back to notice.

My reluctance to use drops was more about the look of the bike. It always seemed daft to have a huge stem riser to create a high point for the stem to attach to, only to fit bars designed so you can have your hands lower than the stem. With bull bars I had a much shorter stem riser and there was a more direct line between the headset and my hands. I've got over this now and very happy with my drop bars.

My next tip is to experiment with tyres if you haven't already. Some tyres will roll a lot better than others and for that sort of distance this is going to be more noticable than for short trips. I've been down my local track (where I race in a track league) doing laps of constant speed on different tyre/wheel/pressure combinations, using my Swift's power meter to measure how much power is needed to maintain the same speed. This takes into account not just the rolling resistance, but how well the tyres roll over the imperfections in the road, and any effect of weight differences in the tyres (the 500m track is not quite flat). I did this test because the Stelvio's I've been riding for years have been discontinued and at the same time my rims have cracked so I have the opportunity to change wheel size as well as tyre. So far I've tested 3 setups with the following results, all at 30km/h:
451/Durano @ 100psi - 221w
406/Kojak @ 100psi - 212w
406/Kojak @ 80psi - 207w
. In other words 406 kojaks @ 80psi need 6.7% less power to maintain 30km/h as 451 Duranos.

I have a pair of 406 Greenspeed scorchers being despatched today that I should be able to test on Wednesday. I can't afford to buy any more tyres for testing but if anyone in the UK wants to lend me a pair I will happily test them (I'd like to test some Comets).

On the tests I've seen that test rolling resistance on a drum, higher pressure tyres always come out with lower rolling resistance than lower pressures, so the fact that Kojaks are faster on my local at 80psi than 100psi is interesting, which to me is proving that the bump-smoothing effect adds to speed (anyone in the UK like to lend me a pantour-hub wheelset to test?). My track is pretty smooth, and I suspect on bumpier roads the 451-size would do better. N.B. my track isn't flat - one one straight I was doing over 300w to maintain the speed and on the opposite straight I needed <100w.

Day to day, my 406 Kojaks I'm now using definately 'seem' faster to me than my 451 duranos did, but a quick scan through forums suggests that the scorchers could be faster still, and being higher volume I might be able get more benefit from the suspension effect at lower pressures.

My final tip for long distance riding is that half the challenge is about food not cycling. This is based on my experience from training for a 12-hour race. You need to experiment til you find food where you can get enough calories on the bike during the ride but so it doesn't slow you down. The lower intensity you are riding the less this matters, but if you are riding for hours at pretty much the max intensity you can, then you won't have much capacity for digesting. For me the magic formula was High5 4:1 with 'SIS Go' gels every 45mins. Having a drink with Protein in definately defeats the 'bonk' for me, and 4:1 was the only protein drink that didn't make me sick (I found Perpetuem horrible) and of all the gels I tried, 'Go' was the only one that didn't slow me down (it's also the only one I tried that is isotonic). It's all personal though - some of my friends doing the same race were happy eating nuts. You need to experiment - It took me 3 months to find the combination that worked for me.