Hi Wheezy,
The thread swislon is referring to is
here I have used my RST off-road several times now. (Off road to me means bridleway or worse) I actually really like the way the RST handles off-road however there are a few limiting factors. (Most notably the low BB height and the tyre clearance.)
If you compare the RST to the Tour and the Nomad you will find that the RST has the shortest chain stay this should make it the most agile of the 3 and therefor the sweetest handling off road. The caveat in this is that the RST also uses the thinnest tubes of the 3 and has the least tyre clearance
My RST is a MK1 short top tube version set up with drop bars. This means it is not compatible with a shock absorbing forks. Most of the time I don't miss them however on rough descents there is no denying the advantage of a good suspension fork.
One final note. the MK1 has (I believe) greater tyre clearance than new RST. I use 1.95 tyres