Hi,
before I re-installed windows I had DirectX 8.1a on my comp. I think it came from the F1 2002 CD, but as I took that back, I can't be sure. I was getting 'below average' (ie, less than what I should have been getting) on GP4
Anyway, when I re-installed windows I had to re-install dx 8.1. I installed it from the GP4 CD (which I hadn't before). I though it was 8.1a, but when I installed Age of Mythology, it didn't ask me to instal 8.1b. It needs 8.1b to run, so the GP4 CD must contain 8.1b.
So GP4 in theory needs v. b, but can use v.a. So it could be that this'll lead to a performance increase. I don't know yet because I haven't installeg GP4 again atm. But for people who are struggling, it's worth a try.
Bye