Thanks again guys for all the advice. I've also taken the advice 9off forum) of a very successfull windsurfer - perhaps you've heard of him - Keith Atkinson. I followed Keith's advice and have gone for the 11.6, 9.8 and 9.0. His reasoning went like this:
the reasons being that the sail (12.5) is heavier, and harder to get onto the plane generally. if you pump well then a smaller sail will pop on the plane quicker. however if your lazy, which i'm sure your not given your athletic background, then a big sail will pull you onto the plane, albeit slower.
the other reason for not going 12.5 is that in the UK the air is denser and therefore has more power in a place like Silvaplana, for example. which is why i said if your doing any international racing like in a place like Silvaplana then you may need a 12.5m. however i, and many other sailors only use 10.7, even in Silvaplana. bigger sails maintain speed better when the wind is really marginal. i opt for the smaller sail i can get away with because its lighter, planes earlier with my pumping, however i struggle in margina; conditions in the open sea when abroad, but not in the UK.
personally i would go for 11.6 as your biggest, then you can either go for 10.7 as a changedown and then down to a 9.8.... or if a 9.8 is too big as your smallest, then go for the 11.6 - 9.8, then 9.0. the reson i say this combination over 11.6 - 10.7 - 9.0 is because the 10.7 is too close to the 11.6 in power, but the 9.8 is a significant enough decrease in size, but maintaines serious power to justify jumping onto it. but my opinion is, it's too powerful for the smallest. the 9.0 is so sweet!!"
Its hard to argue with that!