[nascarstewartfa]

Ok, here goes, I have been thru the ringer trying to decide which cnc plasma system to buy and after running all my options, I have decided to build my own. I am building a 4x8 table, used only for plasma. What type of guides should I use?

[Torchhead]

If it's plasma only the V groove bearings with twin rails (top & Bot) will work fine and you won't have to worry as much about all the nasty plasma dust buildup on the rails. If you ever want to use the table for contact cutting (router, etc) then higher accuracy is needed.

You can run the v-groove bearings down a piece or angle iron but you should expect the lower accuracy that brings. Plasma cutting is not a precision cutting process and you will be lucky to hold + - .020 at the toolpath. Any inaccuracies in the table add to the overall errors.
becomes important. It all depends on how accurate and smooth you want the movement mechanically. For plasma only the gantry can be lighter and you can design around the higher cutting speeds you need with plasma.

I think the matching tracks for the V-grooves would make for a better design.

Honestly your challenge will not be in the rails or bearings. It will be getting all of the drive components to align and mesh with minimum backlash. The motor to pinion needs a level of belt reduction. The Z axis needs attention and there is of course the electronics. Word of advice: make all of your mechanical drive components adjustable so you can square and align things!