Hello!
I am photographer fresh out of school, and i went from the 13" to the 15", and i can say the 13" is waaaaaaaaaaaaaaaaay too small for you, i'd get the 15" plus the matte screen, which offers highler resolution and matte, which doesn't give out annoying reflections and represents colors that are closer to real life.
the 6750m is definitive the card for you if you're into gaming or 3d intensive stuff, i don't think it'll make a huge difference in photography, however, the 2.0 to 2.2 might make when editing tons of photos on LR catalog. The ssd on the 2.2 model is 100$ cheaper(the 128gb one), i have it installed on mine, for once the mac boots up in 20 seconds with adium already open, which is nothing short of awesomeness, programs launch instantaneously. Recently worked with 3 meter long files which had 60 houses cut into it (i can link you if you wish to see it), full 21mp raw files which were inserted has smart layers and the psd file was has big has 18 gb before i dumbed it down. the ssd definitive improved scatch disk speed, however if you want to enjoy faster editing you'll have to import photos to your ssd then move them away to the HDD, like the G-TECH mini i have which has firewire 800 and is sold on apple's website.
http://macperformanceguide.com/ has some tests with photoshop of the new 6750m one with the apple's ssd, and OWC counterparts, ofcourse OWC has faster ssd's but when considering the price of the ssd being 100$ and even counting they're going to swap the drive it still is a good deal, but if you go with the low end, the upgrade is 200$ so i wouldn't get it at that price, also i'd recomend checking his guides to configuring photoshop cs5, or you might suffer performance issues due to bad configuration.
also, you might benefit from having 8gb of ram instead of 4, i say might because it depends how many layers you work with, apple's ram is still way to expensive, i'd get a pair of crucial or counterpart ram (some have been putting 1660mhz ram into macs, and i doubt the average human would notice it but the price diference is so small... why not), mine costed 81 and it is extremely easy to replace, you should check out some youtube videos.
to be honest, i'd go for the low end if i were you, perhaps the 2.2 upgrade might be good for you, but i don't think the faster ati graphics will help you much.
ofcourse you don't have to buy all of this at once, i'd worry about the matte screen, and PERHAPS the ssd and the 2.2 might be a good choice!
edit: i thought you could upgrade the cpu on the 2.0 model but since you can't i wouldn't really worry about it, the 2.0 should be more than fast enough.
hope i helped.