Well we had better start looking on Ebay for some real cheap routers that only need upgrading to supported rails.
That will cover most of the Techno Isel range, Hiez, and all the Brit ones.

I'll grant you supported rails will be far stronger than unsupported, it doesn't take a white paper to work that out [ unless it's toilet paper - non coloured ] but how about doing a paper on what is allowable in a DIY enviroment.

Has any one else ever mapped the deviation on say an X rail as it travels full length due to bed twist, and then done the some on the other rail as it returns back?

Those results will be very interesting. A quick and dirty test on any machine is to do a very fine engraving in brass then run the code again and see what extra metal is removed on the second pas or if it's thinned the engraving down. This is a very good PRACTICAL test.

John S.