How good or bad is the ATI Radeon HD 5770 for Photoshopping?

Question

I'm on the verge of upgrading machines for the first time in half a decade. My Opteron 180 is kinda obsolete and, well, falling apart.
I was leaning towards a Dell Studio XPS 9000. More specifically, an Intel Core i7 920 /w 12GB ram.
During the holidays, these machines came with a choice of nvidia or ATI card. For whatever reason, most of the nvidia options -- the 260 in particular -- have been removed from the build customizing options. In fact, with regards to this one deal I'm looking at this week, the only choice is the ATI Radeon HD 5770.
Here's the link : http://www2.dell.com/ca/en/home/desktops/desktop-studio-xps-9000/pd.aspx?refid=desktop-stu dio-xps-9000&s=dhs&cs=cadhs1&~oid=ca~en~70702~studio-xps-9000-en-feat_3~~
Now considering what a great deal that is, and that I won't be gaming with this machine (so I don't much care about 3D performance), is there any reason why I *shouldn't* get this machine?
I keep hearing about nvidia / CUDA benefits. Are they really worth my passing up on this deal? Because other than the card being an ATI, this machine pretty much suits my Photoshopping / DAW (music) editing needs.
Am I making too much of an issue about the video card, considering we're talking about 2D performance here? One benefit I keep hearing about the 5770 over the nvidia GT260 is that the 5770 requires less power and is more silent.
Opinions?
(PS: Before recommending I pass on this and order from X or Y or Z, please keep in mind I'm in Canada. The choices are different here, and the price you see at that link is CND.)

Answer 1

I am about in the same spot as you, trying to decide what machine to upgrade my woefully inadequate machine too.  I was considering a XPS 9000 however I have about talked myself into building one because I can get a much better motherboard with all sorts of eSATA3, USB3, dual-network-connection teaming and whatever else if I do that; however, it takes a bit of research to get things right and I am at the beginning of that process, so I may give up and fall back and go the Dell route after all. 
If go with Dell, you can get memory for a bit cheaper than Dell will sell it to you so maxing it out at Dell may not be the most cost effective solution.  I mean it might be cheaper to go with the minimum RAM and then sell or trash it and buy your own 2GB chips.  Unfortunately Dell does not have a no-video-card option, but the HD 5770 is good card.
As far as ATI vs nVidia, ATI is the only one with DirectX 11 at the moment, which includes automatic tessellation for textures that have a displacement map.  I doubt Photoshop will care about that although new games will.
Here is the "Heaven" benchmark running on a $700 HD 5970 dual-GPU card, but the tessellation works on the newest cheaper ($150) ATI cards too.  The difference is most noticeable on the walls roof and stone pathways:
http://www.youtube.com/watch?v=rEnl8k6BcDs
Unfortunately Adobe has not given us guidance on what CS5 might need or can use as far as GPU support.