Peronally, I think the low line is the best. Yeah you keep more momentum with the high line but since the corner is so vastly big the longer distance you have to travel on the high line negates he momentum gained in terms of lap time.
In the GT Academy, if I remember rightly the best line was low-mid way up the banking, just above the first set of road markings, and then from about half way very gently turn inwards so that you practically scrape the inside wall on your way out.
I agree with it depending on the car, but I say a car with more power is better suited to the inside line due to the decreased momentum but shorter overall distance. Powerful cars can regain that momentum more readily, low power cars need to maintain it. And here I just realized we're talking about cornering on Route X. Route X!!!
The problems that I find with cornering on Route X is that my GT-ONE and Veyron go 300+ mph, and that they can't turn at all. I have to slow down to 200 with the veyron and 250 with the GT-ONE in order to make the corner at all.