- the FT138 would get you planning in marginal condidition 9- 10 kts with your 7.5
- the C133 and FU133 are quite similar in stability (not easy to fall off)
- the C133 is in comparison to the FU133 a real bore (slow, not very manouverable)
The FT138 can't really be compared to the other 2 boards (the C133 and FU133 will never plane as early or go anywhere as fast as the FT138 in 9-14 kts of wind and fairly flat water). The FT138 is a light wind speedster (pity is you're fast enough to really pop small swell, but if you get a FT138 wood you should be smart and keep it flat).
The question comes down to targeted wind range: from ~ 12 kts on the C133 and FU133 with a 7.5 at your weight can become fun. If you only want the board for 14+ kts -> you should maybe take a closer look at the FU122. The 2008 FU models were a bit wider than the 2009 (my experience is based on the FT138 , C133 2007 and FU133 2008) == they could very well need an additional kt or so to get going (a thread asking the team on this issue went unanswered).
hope this helps