I believe I once asked what was the difference between running BH2 on GC or Wii, and the general consensus seemed to be that the difference would be barely discernible.

Since that time, it was brought to my attention somewhere (cant recall where) that the Red JAP Wii was slightly faster, I believe loading wise. Can any experienced GCN runners shed any light on this? Is it just placebo effect, or does anyone know personally if there's something to it?

GCN doesn't count loading times. So whilst the Red Wii could potentially save time on loading it wouldn't actually save any IGT.

Is the red Wii even compatible with gamecube games? Thought only the first model of the original Wii could do that.

Not 100 % but you might be able to play GC games on all Wii versions if you mod the console.

Wii Mini and last Wii version don't even have GC controller or memory card ports. Is it possible to play with a classic controller when you use Nintendont ?