Is there a reason you're looking for one board to do everything?
I still have my 'beginner' board (142x42cm 2011 Nobile NBL) which I use when there isn't quite enough power for my high-wind TT (135x37cm 2012 Ocean Rodeo Mako). Having the choice between the smaller board to hold down a slightly overpowered kite, and the ability to switch to the larger board if the wind gets light gives some extra range to my kites and can turn a mediocre day into a great one.
Were I in your position, I'd get a larger board for learning and lighter winds (at least 144 in length given your size). Then once you find it's holding you back, you can get a more aggressive board--not to replace it, but to complement it.
For reference, I'm 5'11" and 160lbs. You can check out Jim Douglas' kiteboarding calculator
for guidance, there's a 'BoardSize' tab at the bottom. Boards are now wider for their length than when he wrote it, however. So, keep that in mind.