Teatoo,
I spent some time snooping, I wasn't aware Apple had refreshed the iMac line recently.
Technically, the ATI Radeon HD 4670 has
better specs than Slingsby's ATI Radeon HD 2600 ... it's a newer chipset.
I REALLY think EA needs to update the
The Sims™ 3 Minimum Hardware Requirements, because you're right ... reading there the HD 4670 in the Mac you are looking at is
not listed as a Supported Video Card (but Slingsby's 2600 is).
And The Illuminator pegged it, when a software company provides a list of "supported" video cards, they are just listing the cards / graphics subsystems they are willing to provide technical support for. It's certainly NOT an all-inclusive list of the systems their software will work on, just a list of what they are willing to try and keep their software running on.
Most "graphics card issues" in games is newer software struggling with older / dated drivers trying to work with older / dated architecture. The iMac you are looking at is a "modern architecture" system (Core i3 / HD 4670), and the Sims3 is a pretty new software package.
I really can't see why the machine you've listed here wouldn't run the Sim3 at max settings, right out of the box ("supported video card" or not).
If your still a bit concerned, I'd head over to the Apple forums and just ask if anyone using that flavor of iMac's playing the Sim3. I'm sure you'll get at least one "oh, yeah, no problems."
Hope this helps, and I think you're smart to check this out. A computer's a big investment, and you want to do as much as you can to be sure it'll run the software you want to run on it before you buy it.
In this case, I think EA just needs to update its list of "Supported Cards."
-- Happytime