Well, the wheels that I know of between T66 and T76 are the GT67, T70, GT71, and the T72. I don't know what compressor cover you have and how far it can be machined, but if you were told you could go all the way to a T76 then all of them should be possible. I'm assuming a P trim turbine for all this. In my opinion: the GT67 is so close to the 66 it wouldn't be worth changing, I haven't heard much good (or bad) about the GT71, I've heard that the T66 will do high 10's but it's really straining to do mid 10's, the T72 will do mid 10's easily, and the T76 can be pushed to high 9's or more. So, I would go to the T72 if I were you, and about 3200 or 3500 stall, probably 3500, and 72 lb/hr injectors (I don't think you need 83's but they won't really hurt anything). You could also think about a GTQ trim turbine wheel and a T70 or T72 compressor but that will really need more stall and not be nearly as nice on the street.