A couple weeks ago I was washing my ISF and noticed (finally, I should have seen it a long time ago) that the kid at NTB had put my front wheels on the wrong sides. I went back into NTB and explained my situation to the manager, and he had his most experienced person rebalance the front wheels and put them on the correct side. Their machines can only calibrate balancing up to 60 or 70 mph, so road force balancing is what I will use in the future...and I will never use a shop like this again that isn't accustomed to working with high performance cars and low profile tires.
Anyway, I have had the opportunity since then to test out the car's feel at "Speed". 90% of that floaty feel is gone.
Anyway, the moral of the story is, don't be cheap like I was. Find a good shop when you have new tires put on your factory rims. 245s front and 275s rear work just fine, but make sure they put the correct rims back on all four corners of the car, and have them road force balanced if you ever plan on getting froggy with her.