I sat down and had a big think about whether to go for it or not. In the end I crumbled and opted for 20% off the 500 instead of 20% plus the extra £30 off the 200.
I appreciate that it's not remotely as good a saving, but it still made it a very good price, and I figured that as good as the 200 is, I'd probably pretty quickly wish that I'd invested the extra £s to get the additional features the 500 offers.
I suppose you can say the same about the difference between the 500 and the 800, but I really couldn't justify all the extra cash for that one (especially now my touring buddy has decided to get married - our tours might face the chop now he's under the thumb (and he has a 705 anyway))!!
I just have to figure out what to do with two cateye strada wireless computers now!