If the T-stat wasn't changed when they did the radiator, change it if only for GP (should be simple - 3 10mm bolts, one o-ring and the T-stat. No sealant or gasket to mess with).
I also just read in your other post that you went with 50/50 mix. I did too and had a little warming up issue too. Drop the mix to 70/30 (H20/AF) and I think you'll see a difference.
I'm not sure how much volume your cooling system has, on mine it's about 3.5 gallons. I drained off 1 gallon of mix and replaced it with bottled water.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.