Don't get an X2 4200, it's pointless. If your getting an X2 get either a 3800 or a 4400. The only difference between the 3800 and the 4200 is 200MHz. Which you can easily make up for in an overclock. 4400 however has a 1MB cache on each core vs the 4200 and 3800 with only 512K per core. Also I'm pretty sure that you'll be able to get that Opteron up to 2.6GHz.