Widgit as far as I know I have never posted on one of your build threads but I do have a suggestion for you now. I use an old Digital Tool router, which to my knowledge is the first kit machine offered in the US or maybe the world.
It uses rack and pinion for the drive motion and dual vee wheels and v-rail for the rail system. I have run this machine thousands of hrs and the only problems I ever had was a design flaw. I have never had a problem with the r&p nor the dual vee wheels. TEA is a company that advertises here on the Zone, take a look at the vee wheels. I don't think you will be dissappointed.
I hoping to build a machine between now and the first of the year and it will in all likelyhood have dual vees and a belt drive......just because I want to try it!
Mike