You are windsurfing on a lake in mostly light conditions. You are in an improver stage, and can benefit requally well from light wind and high wind training.
The Futura 133/144 are surely good boards, but only if there is enough wind for planing. If the wind is too light then they are real dogs.
It is hip and trendy to pick a board without a centerboard, but I do think it would be a mistake. Starboard has two ranges of boards with centerboards. The Rio has changed VERY significantly from 2007 to 2008. The new models are up to 15 cm narrower, and up to 35 cm longer. This means that they have much better glide in light winds than the older boards! If you pick a Rio, go for a m2008!
However, I do still think that you would benefit the most from a Phantom Race 320. It will make also lightwind days interesting thanks to a big dagger, offering more glide being longer and narrower. And it will be perfectly "Shortboardish" in higher winds! Or, alternatively, the Exocet KONA Style/ONE.