For polishing and buffing metals I use a professional Baldor 3600 RPM pedestal buffer.

Baldor makes 1800 RPM buffers too for plastic.

For about $100 more, they also make a 2-speed unit that can do both.

I probably would have bought one of these if it would have been available at the time I got mine years ago.

If you are looking to do some serious polishing/buffing of metals though, you want a 3600 RPM buffer with two 8" sewn buffing wheels (one agressive and one fine) along with an asortment of rouge. I use mine on a lot of stainless parts and some steel and aluminum too. I don't buff a lot of plastic but it would be nice to have the optional slower speed anyway for occasional use.