Well more specifically. aluminum headed 5 liters. I've always shot for 180 degrees but my life would be a lot easier if i settled for 210 degrees but i always thought that was just a lil too hot on aluminum headed cars.
210* shouldn't be too bad for alum heads. You don't wanna start creeping up from there however. I find that when it's over 100*F, it's hard for me to keep temps under 100* over ambient. I.e., if it's 110* outside, I run at 210*F. The air coming off the hot asphalt is probably 130-150* and there's not much temperature differential there between ambient and operating temps (with regard to exchange across the coil).
If you're at about 90* right now, I'd shoot for just above your t-stat rating. This little BS tech note might bring up a few reminders of things to check over and consider.
I'm waiting with bated breath to see how high my coolant temps. will go when it gets up to 115- 120*F this summer. Right now my gauge stays on O driving on the highway at 80-85mph (~3000rpm) at an ambient temp. of 95*F.
I have the stock fan set-up and control but I noticed that the low speed fan comes on about 10*F earlier after I installed an external Hayden tranny fluid cooler and bypassed the heat exchanger in the radiator. Removing the heater tube assembly from the intake manifold and installing a Breeze Automotive ECT elbow kit also helped further.
The fan used to come on when the gauge was on M but now it comes on when the gauge is between O and R. It goes off again when the gauge is between N and O.
i had a 160* when i got my car and that just didn't work for anything. put a 180* in there and have been happy ever since. if your worried, get an aluminum radiator and put the fan on a manual switch. and get an actual temp guage so you know whats going on. i just don't trust those stock ones.