I suspect the good track near you is HPR east of Denver?
I drove my s28i there twice, and didn't have any braking trouble after 20 minutes runs.
I was driving it as hard down the straights as possible, and hit a little over 90 mph on the front straight down to 30-40 for first corner.
What I've noticed when I ran with traction off is the traction seems numb, and left rear spins wildly even when coming out of corner with weight on drivers left side.
So I enjoy the traction control and rear brakes are wearing faster than front.
Your x28i has all that brake vectoring claim, so it might be running more than necessary and heating brakes.
I'm not having any fade ever.
I think I'll put rear pads on and see how it works with fronts until they need it.