For the track (road racing my FFR), I geared 4th for the longest straight I will encounter. (Actually, I had to use 5th at California Speedway, but that is another story.) 1st is used for starting. 2nd, 3rd, and 4th are used for the road course. I am almost always in 3rd and 4th. With a lot of HP to weight ratio this works well. 5th or 6th are just cruising gears. Or maybe you want to make some sort of high speed run in 5th. Unless you are in a serious competition where you will change gears for every course, (I know of no GT currently like this) what we have is fine.
The GT really doesn't need that 6th gear. It is there for CAFE standards or bragging rights because so many "exotics" have 6 speeds. But most of those "exotics" do not have the power to weight ratio of the GT.