Which ones will be quicker?
There is nothing there that I don't use and it never maxes my 2.66 out :/
BTW, why is all that so expensive?! My 2.66/1Tb/6Gb/4870 was £1900, so even if you get rid of the HE discount its still £2200...

Edit: Oh the applecare is well expensive for non-HE, nevermind
Add the 2nd 1TB yourself, get a 300Gb Veloci as a boot drive.
As for the specs, the 2.66 is the best bet IMO. The 2.26 will show its slowness in single threaded apps and games, the 2.66 will be 2.93 after Turbo Boost (although i've only ever seen it go to 2.8 :/)
MPs hold money very well, save the money, see how it goes, and in a years time when the next lot come out, you could very well be using 16 thread apps and thus the 24 thread Mac Pros may be better for you
8Gb is more than enough at our levels IMO. (I use Xcode as well btw, forgot that bit

)
But ultimately up to you:
1. Pretty much same spec as me, handles everything I throw at it fine.
2. Faster CPU, more what your used to, 13% increase in cost for a (what I was thinking about at the time a 5-10% increase in performance)
3. Slowest for what you are used to, highest overall power, but that list of apps and that SLR its a waste (and a BIG drop in games)!