When you guys are casting bigger bullets (in my case 400gr .475) what temp do you usually cast at?
Last night I was getting some of my best bullets ever & was warmer than normal. according to my RCBS thermometer I was running a bit over 860*. Using a Lee double cavity mold, casting as quick as I can. Fill, 20 sec wait, cut sprue, dump in 5 gal bucket of water & fill 'er up again.

That sounds a tad high, I usually am 700 to 750. But if it works for you with the alloy that you have, go for it. I have to adjust my pot frequently while making bullets.

There are a lot of factors involved when determining the best temperature to set your furnace to. It looks like you found the best temperature for the conditions you were casting in. There are no hard and fast rules. If someone says you have to be at least this temperature, or no higher than this temperature to cast; you determine what works for you.
One thing about those great LEE aluminum molds, they don't seem to care how hot it gets.

Each situation can be different, or at least it is for me. Sometime with the same mold and alloy my optimum temp will vary 25 degrees. Steel, brass and alum molds all seem to have different preferences, also.

Just fiddle with it until you get everything as you want it and try to maintain that temp.