Which Imac 20-Inch should I buy?

I'm trying to decide on which Imac 20 inch refurbished I should buy. They both cost $849.

The first one has the intergrated Nvidia 9400 chip (FB417LL/A early 2009 model)

The other one has the ATI Radeon HD 2600 XT with 256MB of GDDR3 memory (FB324LL/A I think this was just before the other one)

They are both 2.66 Ghz and I think the Nvidia on has an extra USB port and uses different type memory or something.

I would think that even though the ATI Radeon Imac is older that it still is slightly better since it has a dedicated graphics card vs the intergrated Nvidia. Am I right about this? I would imagine all you gurus over on this forum would know better than me since I want to make sure I'm not losing anything by going with the dedicated Graphics card or over the Nvidia.

I use Adobe CS4 and plan to put it on the machine and I like 720p & 1080P video.

I would appreciate any input.

Thanks

I know that the one with the ATI card has the sam 2.66 CPU as the Nvidia but the ATI computer takes 4GB of RAM at the most as opposed to 8GB for the Nvidia one.

I imagine 4 GB of RAM should be enough for my CS4 if I'm not doing huge files and editing HD movies. Is this right? I imagine the better dedicated graphics ATI crad trumps the ability to add more RAM in my case.