U know what? I was actually thinking of a Radeon HD6670/5670 for this matter!
It won't require extra power, rather than from the PCIe slot & it's fast enough for 3D, but not as an enthusiast one.
I don't do any Cad yet... might have to in the next few years perhaps, but I'm sticking to Vectors & Rasters now, so, something like an entry desktop video card is enough for now I believe.
BTW... how about a Radeon 54xx/64xx or even as low as a 63xx/63xx? Do you think they might be even fair for PS/Ai?