Im gonna ignore all the 5GTT vs. F7 engine nonsense - apart from to say that theres no substitute for capacity, as Ben so eloquently put it, an extra 400cc and 8 valves makes a big difference if its turbocharged the same.
The thing Im more interested in is why you would want a turbocharged motor if youre building a track day car? Id want a highly tuned NA engine for track work, not a turbo. I drive a turbo valver because I want a bloody quick road Clio and it is, plus it serves my purposes on the 1/4 mile. But the characteristics of turbo power delivery are definitely not what you want on a track, NA is the way to go.