Most of the time you just need to look at the chipset. The newer HP/Compaqs often use a very good chipset in their upper models. Now you will have about zip in the overclockability dept, but these days overclocking isnt worth much.
I can only say that often you can get a better deal on the AMD chips. $1200.00 and it'll scream....Ive got an older single core amd 64 3800+ w/6800gt and its a monster.
I will tell you you'll want to look for a good CPU heatsink...cause the HP ones work very well....you can tell by the screaming jet engine sound comming from the case

price $1,344.00 *
mail-in rebate − $150.00
price after rebate $1,194.00
you saved 11.2%
as low as $40/mo+
12 months no payments. Apply now.
Estimated build date:
September 20, 2005
Monitors and add-ons are in stock and ship immediately.
Click "edit" to modify your customized pc order.
Operating System Microsoft(R) Windows(R) XP Home Edition with SP2
edit
Processor AMD Athlon(TM) 64 3800+ operating at 2.4GHz
edit
Memory FREE UPGRADE from 512MB to 1024MB 400MHz (2x512)
edit
Hard Drive 160GB 7200 rpm SATA Hard Drive
edit
Primary CD/DVD Drive FREE UPGRADE from DVD-ROM to 16X DVD+/-R/RW
edit
Front Productivity Ports Front USB, FireWire and audio ports
edit
TV & Entertainment Experience None
edit
Graphics Card 256MB DDR NVIDIA GeForce FX 6800, DVI & TV-Out
edit
Sound Card Sound Blaster Audigy 2 ZS for MS Home or Pro OS
edit
Keyboard and Mouse HP Keyboard, HP Scroller Mouse
edit
Productivity Software Microsoft(R) Works 8.0/Money/MSN Encarta Plus