Ill say that depending on the features you need, both processors will work just fine, if you are worried about price of your GPX card on the xeon, i would go i7 but i would reccomend cheaper still.
take a look at the i7 960 minor differences from the i7 975 extreme for half the price for example -130mhz clock speed and a 4.8gt/s difference also the BUS/CLK ratio is 24 instead of 25. these differences are not even going to be noticeable, especially if you overclock it.
and as far as your xeon the only technology that the other two do not have is demand based switching, whether or not thats important to you will be your decision.
here is a link that you can compare:
http://ark.intel.com/Compare.aspx?ids=39719,37153,37151,
As for another reference for you take a look at this article it might help you out a bit.
http://www.tomshardware.com/forum/271131-31-best-heavy-video-editing-nehalem-xeon-opterons
if you are really familier with overclocking then an i7 920 would be your best bet,
as a closing question how intense is this photo editing? are you video editing?
message me back if you have any thing you need to ask