I don’t know what the spec is you’re after but check out compatibility for the NVIDIA geforce 9800 gtx or one of it’s close siblings. I bought 2 of these recently and they are good at 3d modeling. Cost is around a couple of hundred $ (IIRC). I bought them from Dell after checking that they were compatible with the computer (hint)

There are a lot of good video cards that do 3d that aren’t that expensive. The FX 3500, as example, sells for around $400. Do a little shopping for something that matches the stated spec.