The Mainconcept "standalone" MPEG encoder has many features not found in the version included with Vegas, including 2-pass encoding. Some report that it produces better quality at faster speeds. There may have been some tests posted in this forum, but I can't remember. I don't have it myself, so I can't give you actual measurements. All I can tell you is that it is different, and it does have more features.
I recently tried the demo of mainconcepts mpeg encoder 1.4. It encodes about 5 times faster than VV4 and the quality is better. I couldn´t find a way to update the VV4 mpeg-encoder, though.
The MC stand alone encoder is faster than the one with Vegas but........as with everything there is a trade off. In order to use a Vegas project in the stand alone encoder you must first render it to an AVI file. With Vegas....you can just render it straight to MPEG. Therefore the time you save in the stand alone version is negated due to the AVI render.
As my dad would say...."6 of one and 1/2 dozen of the other".
You want fast....check out the Cinema Craft Basic encoder. It flies!
Yes... You can frameserve to it.
I tried it. It worked and still seemed pretty fast. Seemed like a really good
way to get better use of multiple processors too... but no one with multiple
processors took me up on the idea to try it and let us know how it went.