I have both the 990Xa-UD3/FX-6100 and the 990FX extreme4/FX-6300.
Both are excellent boards.
I have had both of them up to 5Ghz and are currently set to 4.8Ghz.
I also have RipjawsX series 2133Mhz ram in the Extreme4 running at 2133.
I love this board especially since it sports the older IDE interface and is the reason I got it.
I haven't had any issues with either of them yet and I am running a dual boot system with Win7 and Ultimate Edition Linux on the FX-6300.
I can pop in any one of my older IDE drives and access my archived data at any time.
jer