Forza beat GT4, so it's most certainly possible. However, Forza had a few advantages last time that it doesn't have this time. If you recall, GT4's online mode was removed shortly before release, and the Xbox's more powerful hardware gave Turn 10 quite a bit more headroom for their physics implementation. Plus Forza had damage, while GT did not.
Given the fact that both games will have damage and online this time around, I think overall content will become the prime differentiator. From what we know so far, this will lead to GT5 having the higher scores (because of the variety of cars, GT TV, Top Gear, etc.).







