I did my semi-annual reformat of my hard drive recently on my PC at home. As part of re-installing the latest versions of the programs I use I found that my CD-ripper, AudioGrabber has gone freeware! This was welcome news. While at their site I noticed the the FAQ said the fastest MP3 encoder was Xing's MP3encoder. Of course, it costs $19.95USD while many others are free but I do these things so you won't have to waste your money.
So I paid my money, downloaded the 1.8MB file, and ran the installation program. AudioGrabber uses the Xing encoder as an external program but has default parameters set for it so all you have to do is point AudioGrabber to where the encoder is installed and you're ready to rip.
I chose Diana Krall's rendition of "Let's Fall in Love" as a test file. This song is 4 minutes and 17 seconds long and creates a 43.8MB wav file when ripped in stereo at 128Kbits/sec. My test PC was a Dell OptiPlex GX260 with an Intel Pentium 4 running at 2.66GHz and 512MB of RAM. I ran three tests each for Xing, LameEnc 3.96, and Ogg Vorbis 1.0 and averaged the results in seconds and the resulting MP3 file size:
Xing 23 seconds 4,020kb
LAME 36 seconds 4,020kb
Ogg Vorbis 38 seconds 3,957kb
Clearly, Xing was indeed faster than the other two encoders and if you rip 60 minute long symphonic works perhaps the speed difference is worth it. But I will leave it up to you to decide whether the $19.95USD cost is equal to the 57 percent or 65 percent respective speed increase. YMMV.
Aloha!