If your main use is photo editing then might consider a E8200 + Gigabyte G33M-DS2R for $497 @Fuwell at SLS.
The board is micro atx board with a onboard X3100 graphics. This board can Oc'ed better than the P35 and X38 chipset which can go up to FSB 440-450Mhz at most.
Can check full spec of this board at
www.gigabyte.com.tw
The E6xxx processor is built using the older 65nm tech while the E8x00 is the new 45nm tech.
CPU speed is 2.66ghz but can easily push to 3.8Ghz with DDR2 PC8500 (1066mhz) Ram Module using settings clock multiplier 8 x 480Mhz front side bus with normal cpu cooler.
One bugger even did a 8x600Mhz = 4.8Ghz but I'm a bit skeptical.
See here for benchmark at actual speed using Photoshop CS3 :
E8x00 vs E6600 and
Another E6xxx vs E8x00
See E8200 @4.8Ghz here :
Extreme overclocking at 4.8Ghz
Actual you'll do fine overclocking a E8400 to 4.2Ghz (9x470). Why overclock ? bcoz it translates to more work time savings.
If u need to play extreme gaming on the rig and if budget permits add a ATI HD3870 X2 1Gb. It's :thumbsup:.
I will be making one myself a couple of months from now.