I think a 1" rod of 6ft will bend no matter what else happens, just not stiff enough!
The deflection over large distances IS the main problem with router tables etc which is where the open linear bearing come in so you can increase the height of the side plates to limit deflection etc
Most of the professional units have the running gaer fixed in some way to a 6 legged table and all this does not come cheap.
Have you thought of using simple bearings running against some square tube or some such, a cheaper alternative.

peter