I tend to agree with Kerry about upgrading your CPU as the only way to really increase encoding (or transcoding) times.
A dualcore PC would be sufficient for what you want to do. Just as an Example, I had a Intel E6600 Core2Duo and that system was able to get ConvertXtoDVD to finish full DVDs (from any source, including from Bluray m2ts files), in about one hour. It won't help to go to a QuadCore unless you plan to do full on encoding with something like x264, then it would be twice as fast as even the Core2Duo, but the QuadCore only gets ConvertXtoDVD to finish in about an hour as well, because ConvertX doesn't utilize all four cores unfortunately.
So a DualCore (Intel or Athlon) would be sufficient and one hour or so would be the fastest you'll see with ConvertX.
BTW, Nero Vision Express sucks IMHO... ConvertX will give you better PQ, especially if the source video is of higher quality to begin with like an m2ts file.
If you haven't purchased ConvertXtoDVD yet, and are only trying out it's free trial... here's a link for a great discount... it's where I got my ConvertX...
ConvertXtoDVD for $29.99