Canon 1D Mkiii..... 21Mp, full-frame (and no crop factor - it's the 1D Mk2N that has the smaller sensor, with the 1.3x crop factor) (the link is to a "1D
s Mk3" - note the small 's'..... if that's what you're looking at - it makes a big difference!). the link doesn't mention the onboard processor but you say it's Digic3 - I can't think it will make a lot of difference, particularly as you mentioned low-light photography (and high ISO) isn't a major factor. US$3.5 on Amazon.
Canon 5D Mk2... 21Mp, full-frame (no crop factor) Digic4. US$2 - 3k on Amazon.
If it's between those two, the 5D Mk2 is the better buy - not counting any further upgrades you might need (like battery grip).