Hi just bought a 03 315 with very little use ,how would it compare to an 06 beta or similar ?

Horse for courses really. There won't be a lot in it.

Mind you if you've bought that mint 03 off ebay I'd keep it in a bag for a few years!

I did buy it , i have been looking for a while for a nice one ,my reasoning being the perceived reliability and build quality of the Honda input and i didnt fancy a 4 stroke , but like you say horses for courses .

brilliant little bike you wont regret buying it. mines a 98 and i wouldnt change it for love nor money. oldest bike in our group of 6 and always the easiest to start. every one thats ridden it comments on how soft and manageable it is off the bottom yet it'll pull your arms off when it gets goin!