This topic always seems to spark a huge debate with everyone chipping in their two cents and this thread seems to be no exception. I'm just thankful this hasn't turned into a flaming war with all kinds of name calling and manufacturer bashing (actually, seems kind of unusual for us
Anyways....
This is Agent we're talking about here, so the system will most definitely be used for gaming. When it comes to gaming performance, nothing touches an Athlon64. You don't need to go wild and get one of the FX series, I'm talking about a regular Athlon64, specifically the 3400 or 3200 varieties. They will give you the best bang for the buck.
So let's assume the P4EE and the AthlonFX are out of the picture due to their high cost...
Look at these
gaming scores from Anandtech. Aquamark is a virtual tie across the board, same with Halo and GunMetal. These are DirectX 9 tests and are most likely video card limited.
On the next page, we see DX8 games and some of the differences start to show through as the video card is no longer a bottleneck. Again, assuming the EE's and FX's are out of the picture, Athlon64's take the top three spots by a pretty significant margin on the Unreal Tournament tests. They also take the top 3 spots in Warcraft III, although not by as big a margin this time.
Moving on to OpenGL performance, the Athlon64's continue to come out on top. First up is Quake III Arena, an old game, but it scales
very well and because of its age, isolates CPU performance better than more modern engines, not to mention that there are beaucoup games based on the Q3 engine. Quake III has long been a stronghold of the Intel camp, but with the introduction of the Athlon64 all of that has changed. Still ignoring the EE's and FX's, the Athlon64's take the top 2 spots in this and the top 3 in both Jedi Knight: Jedi Academy and Wolfenstein: Enemy Territory.
Regarding your upgrade paths,
see this article about AMD's upcoming core upgrade. It looks like the L2 cache is being cut in half to 512KB, but there will be about a 200MHz core speed update. This can have a negative effect on content creation and encoding, but should not have too much of an impact on gaming performance.
In the end, it comes down to your preference, but given the information above, and the lower price, I think the choice is fairly clear.
