What type of file do you export to the plasma table? DXF?
If so... risky. I wouldn't trust an export from RVT to DWG or DXF, especially to a plasma cutter.
You can do collision detection with Revit-->Interference Check.
Whatever the minimum specs are...quadruple them.
Revit currently is in the works to utilize multiple cores.
High end graphics cards aren't too important unless rendering.
8G ram-->good 16G ram-->better
There are many post of discussions about system hardware.
http://www.google.com/search?hl=en&rls=com.microsoft:en-us&rlz=1I7ADSA_en&ei=qSDWS4WrKpStrAextND3Dg&sa=X&oi=spell&resnum=0&ct=result&cd=1&ved=0CAUQBSgA&q=system+requirements+for+revit&spell=1
As the software annually upgrades more and more CPU power is necessary to facilitate.
I would be on the safe side and prepare for it.
This would be wiser than upgrading your hardware every time there is a release (which has been typical so far).
"It's hardware that makes a machine fast. It's software that makes a fast machine slow."