Temps can easily get past the 1200s if you run a blanket, I aim for a shutdown temp under 400. If you drive with for a while and let it cool down then it won't have to idle as long. The times I provided are based on my car in my climate at idle. Synthetic is better than conventional for thermal resistance, look at zddp additives. They offer the best wear protection but have been reduced for emissions and emission equipment (cats, O2 sens)