ResilientMike, I try to keep flat foot shifting for the track, like you said, in lieu of the tranny. However, it finds its way to the streets too often, its just too much fun for me.
What I have been doing lately, if I decide to drive spirited, is just let off part way. Its not as tough to tackle, saves the powertrain some, and the shifts dont have to be as violent. I just cant stand how long it takes the car to recover between shifts. Almost 100% of the time I shift this way I experience no grinding at all, shifting at 6k.
As far as the identicle drivers/cars and testing each method... Ive made many runs with my dads 2000 Saleen Mustang. A friend of ours rents a local track from time to time and we spend the day pounding on the cars. My quickest time ever with the car was 13.4. Flat foot shifting 3rd is very tough with this car because of the shifter, it just doesnt like to slide in, it requires a lot of guidance. The one time I was able to manage this, I ran the 13.4. Every time after that, I quite trying to FFS 3rd because I kept missing. My best time since is 13.5. 1st to 2nd, FFS. 2nd to 3rd, granny. 3rd to 4th, FFS. Before I started FFS the car, my times were considerably higher.
My MS3 has never been down the 1/4 without the pedal ever being lifted (except when a shift was missed). Its the only way I will race a car that I am comfortable in. If done correctly, it will turn a faster time, every time.