I am trying to decided between a FirePro V5700 512MB vs Radeon HD 5850 1GB, both video card are with in $20 so cost is not the issue.
This is for my work computer and is used with AutoCAD 2008 and VisualCADD. I do have some rather large files but it is due to number of pieces and not due to complex renderings. I design all of my projects in 3D but I only use the standard 256 colors.
I believe my current video card is having problems because drawings simple 2D drawings are crashing(been doing these kinda of drawings for the last 2 years). The crash usually occurs when zooming in an out and if I am quick enough I can save the file before the cpu and ram usage goes 100%.
CPU: Intel E8400
Ram: 16 Gigs of G.Skill DDR2 800
Video Card: Radeon HD3850 512 - getting degrading video memory card error
OS: Windows 7 64 Bit
Monitors: Dual 22" @ 1680x1050 each
The big thing. Check to see if the Radeon is certified for AutoCAD. If not, definitely go with the FirePro.
Also don't just go on the technical specs - get some side by side benchmarks if you can find them, for AutoCAD if not Visual CADD]
Check out this story on icrontic which compares the FirePro (but the top of the line) to the Radeon 5870
He doesn't compare AutoCAD, but it does show that the FirePro line is pretty heavily targeted toward professional apps, rather than gaming (the Radeon target market). Soft-modding is not a solution either - you don't get the reliability (as in you get crashes).
So do some research beyond the technical specs, which can be misleading. Ask people to run a particular test with their Firepro or Radeon cards. Someone definitely has one of each, so you can hopefully get some kind of comparison.