Monoog,
sorry didn't see you latest post.
I got the R35, the biggest one. Why because 35 Litres still isn't alot and even if you don't fill it up you can clamp it down real tight with the pull straps so it doesn't flap about even if its part full. It has main comparment, which stands well to water, it has some side pockets which are TOTALLY water proof and is adpatble. The harness is great you don't even know you have it on and the harness has two pockets in it which are handy for documents etc. like my passport, toll cards etc.. But the harness pocket isn't waterproof.
To be extra safe, I also got the US waterproof liner. And I got the neoskin helmet bag.
Try to find a dealer who sells them where ever you are living. It's a British firm and I'm living in Singapore and found a mountain bike shop selling the full range CHEAPER than what I would have piad if I bought them on line direct.
Anything else just feel free to ask.