Gerry:
If you do decide you want or need to sell one I would suggest running both through all your turnouts and crossovers and see if any have trouble negotiating the turnouts - like sparking ( the locomotive despite specs saying it can negotiate a specific curve still has problems with that radius turnout) or losing sound (roller spacing on tender especially on crossovers) etc. That would be the one to sell. If they both run well then it is back to square one.
PS - I have a Lionel Northern which specs say can negotiate O54 curves, and it does on simple O54 curves but for some reason it tends to spark when going through some O64 turnouts.
Joe