I had a GM dealer recommend replacing the Dex, I don't know what they put in but its green. Biggest difference is the service interval (Green needs flushed every 30,000 mile they said). The debate is that old Dex is corrosive and ruins a lot of gaskets, and I believe it.
It hasn't run any hotter, but then again it is still winter. The thermostat is the same one and the temp needle still sits the same place. I have never heard the cooling properties are much different, both are a 50/50 water mix (assuming change intervals are observed and corrosion doesn't take over).
The other thing is, the effect of Dex if it gets in the oil pan (not that it ever happens
). They say it is acidic and damages bearings worse than other coolants would. Same thing if the overflow bottle empties and air gets in the system. Dex is worse for some reason when air mixes in.