RE: Go170 vs. carve162 early planing
2 cents from a non-formula sailor. If your primary conditions are pretty much always less than 15 knots flat water & you want to maximize your quality planing time consider going formula.
One sailing site I go to is typically lighter wind that I can sail 8.0 on a larger free-ride. However, it's typically back & forth & jibe with some upwind potential if it picks up - this is nice for the occasional relaxation day. The formula sailors can go deeper upwind, downwind & faster. You said above you wanted more interest in your sailing & this may do it. The reason I haven't gone formula is I usually have other windier options & formula for me also means a whole new sail rig - so maybe in the future.