Strange you say that...
From all the benchmarks/comparisons I checked, it looks like the GT 630 is about 1.5 times more powerful and GT 635 is 2 times more powerful, than the HD 4000
in what? gaming?
in using solid works the difference is less than 5%
for what your doing . . .not worth it.
edit: i have been using photoshop for several years; there is no difference when i used a GT 8500, 9600 GT, 550ti or GTX 570. your rendering an image . . nothing taxing on any GPU.