hey all, thanks for taking the time to reply. the chainrings up front are 39/52. All that needs changing at the back is the spacing. it's all go for 8 cogs, but the previous owner had it set up with 7. I had the bike given the once over at my LBS and the mech there asked if i wanted to add a speed on as there was the room and the RD allowed for it.
so i'm thinking a 12/26 might be the improvement over the 13/24 on there currently. basically looking for the easy option on the hardest hills if i run out of steam, and a slightly faster option at the other end. miamijim, i don't think i can spin 100 for extended periods on the 13T, but i still want a bit more acceleration at speed there.