I was looking at both of those boards...but for budget reasons, I ended up going in a completely opposite direction.
Anyway, One of my concerns was compatability with my older hard drives. I have 2 high capacity ATA-133 drives. The 990FX Extreme 4 actually HAS an IDE connection on it. (and a floppy drive connection) So if that is important to you, get that one.
Otherwise, I'd go with your choice of Gigabyte GA-990XA-UD3 with 8350/8320.
You're probably going to get about the same OC from both of them, but you're looking at flipping from an 8 'core' cpu down to a 6 'core' cpu if you go with the asrock board.