I full time and my Norcold has been set on #6 since new. It runs 24/7/365. The first one failed a bit over a year ago (it lasted almost 4 years before a coolant leak) and the replacement is still set on #6. I don't have a problem with cooling. Both units cooled fine in both the refrigerator section and the freezer section. Obviously the freezer doesn't make ice as fast as a residential refrigerator, but then a resi refrigerator doesn't run well on a 12v battery and propane.
I'm happy with my Norcold.
2006 GMC 2500HD CCSB 4x4 Duramax/Allison, Titan 52 gallon fuel tank, Prodigy Controller, B&W Companion Hitch
2010 Jayco Designer 35RLTS, Cummins/Onan RV QG 5500 EVAP, Progressive Industries EMS-PT50C, TST Systems 507 TPMS, RV Flex Armor Roof