General update for anyone curious:
I built a little test rig to run each wheel under a dial indicator to check for flat spots or uneven POM material. They were actually better than I thought they'd be with only 5 of the 21 wheels I have on hand being out enough to avoid using. Interestingly I did discover some of the slots on the aluminum extrusion to be pretty bad. I know there is actually a pretty wide tolerance range for these things, but didn't think it would be as bad as it was (one had a bump of nearly 0.5mm right in the middle).
I finished up the design of and printed a new Z-X carrier system that also allows for mounting of the extruder assembly as a bonus. New X-carriage that is vertically mounted as well. Each carrier relies primarily on 2 wheels to provide a motion guide, with the 3rd opposing wheel under very little compression. Every seems to move pretty well, but haven't had enough time to finish assembly yet. Hopefully in the next couple of days I can get it together and knock out some testing. Really a matter of wiring at this point, and getting some mounts done for a MOSFET and some TL-smoothers.
I did order some PA (Nylon) wheels of AliExpress as well, see if they turn out to be any better. I still feel like these are a viable option, especially when you factor in cost, as everything has weaknesses and issues with manufacturing tolerances. If I can get things working well enough there may be a QuadRap design using wheels and t-slot posted here in the coming months.