From what I gather their networking where you work is probably pretty well structured. Pro does that better, handles domain authentication if they use that, and Pro also does multi processor support, as does Parallels I believe.

Get at least 8G of RAM if you can. Allot Parallels at least 1024M in its prefs. It will actually use quite a bit more real RAM than that, but will run better, and the machine will run better with 8, especially if you are doing any graphics on it.