caqde :
Autocad (especially the 2D stuff) and blender don't benefit to much for Pro cards performance wise (especially given blender is open source). Solid works would and is best on a Quadro but bang for the buck would likely be the W5000 or W7000 Firepro from AMD performance wise. (The Fastest Nvidia cards are in the ~$1000+ category).
If you have a multimonitor setup you might be able to designate a gaming monitor and use one of your Gaming cards connected to that monitor (have windows designate it as monitor 1) and you could still keep your FPS in games on that monitor. You'd have to have your viewport on the monitor connected to the Pro card but it would work.
You can run two separate different graphics cards in the same computer?
I have dual 7870's sitting on top of my desk right now, barely used, since I got the 770's. Could I run crossfire 7870's for my rendering for now, and my 770's for gaming? Or could I run my 770's and add a 7870 for pushing movies and such to the tv for the kids? As now when I am watching lets say dora on the tv using vlc, as soon as I start rendering or gaming, the tv screen flickers and vlc either freezes or crashes. If I could use two cards separately that would be awesome, but I always thought that the drivers being separate cards would clash with one another inside windows.