RE: Sails comparison
The TR-1 race sails are very nice, but for early planing on a gusty lake they may not be the best choice.
The 10.0 m2 TR-1 is definitely a formula type design, so it probably needs a bit more pumping (due to less static draft) to get going in marginal winds.
Nearly all top of the line race sails are similar.
The designers expect them to be used by very fit and skillful sailors who have the skills to pump them onto a plane in conditions many of us more "normal" sailors won't be able to get going very easily.
The Retro, Gator, and NP V8 (if you like cams) have significantly more "static draft depth" and can pull you onto a plane far more easily with very little pumping required in the same windspeed a race sail is going to need pumping.
But, as in nearly all things "windsurfing" there's a trade off here.
The flatter profile of the TR-1 race sails will allow you to go upwind higher, and provide higher top speeds. Teh cambers will allow you to sail the TR-1 very overpowered as the cams add stability.
Unfortunately, many race sail designs do not take very well to being "under rigged" to give them more draft.
The Free Race designs (Retro, Gator, V8, V6, GTX and others) have more static draft, and most can be slightly "under rigged" (less downhaul and a fully slackened adjustable outhaul) to make them even more powerful in marginal conditions.
You do have to retune them to take advantage of the full range. For higher wind, they need more downhaul and outhaul to give them better overpowered stability and range.
As far as a smaller board, will you be sailing it on your lake...?
Is the F Type 158 the only board you've had experience on?
A smaller Carve or perhaps an Isonic would be pretty good here.
The S-Type likes 16 knots and up really well.
I'd look for something in the 110-120 liter range.
It will be quite different than your F-Type right at first, but with a short "learning period" you should be able to "transition" to a smaller slalom/freeride type board quite easily.
Hope this helps,