I use a surfboard (6'0 North Rocketfish strapped and Salomon Noseless strapless) and would stay that a surfboard is well worth having in the uk if you have any kind of hankering for waves. So if you have a surfing background or windsurf in waves then you will want to do the same with a kite. I use my surf boards more than my TT in the winter and the other way round in the summer but overall use the surfboard more.
You certainly can use a surf board over 25mph - I use my stapped board with 7m flat kite/ 20m lines in 30/35kts. I can start using the 7m in about 18kts so I would suggest short lines and a 7m are almost essential if you want to use a surf board (I'm 85kgs).
I don't think it matters too much what board you get just as long as you get one and get out there. You can only find out yourself what you like and what kit you want. I've been using surfboards for 5 years now and still don't really know what is the best surfboard for me. Every year you try new things and your ability improves so it is a bit of a moving target.
My personal findings so far:
1) Big boards that you can also surf EG Converse 6'2 Slingshot 6'2? - Excellent for clean waves but not much good for anything else (we don't get clean waves very often!).
2) Onshore slop boards - Airush choptop, North Freestlyle fish, Salomon Noseless. Really good for **** waves, no good for larger waves. Need some skills if you want to ride these boards strapless which is where they excell.
3) Power carving boards - North 06/07 Rocketfish 5'4 5'5, Naish 07/08 5'10 - narrower, smaller boards - good for powered surfing but not very "surfy".
good uk boards as waves don't have much power unless you are facing the atlantic. Good option for someone coming from TTs.
4) Allround board - North 08 6'0, Naish 6'1 - Bit like 3) but more "surfy"
5) Custom - great if you know what you want.
I've riden some of these boards, but not all, so don't get hung up on each individual board - I have just tried to give an idea of board types as I see them.
I sense you hanker after the surf so just get any board which isn't too small and isn't too big (eg 5'8-6'0).