Pumps will feel tank temp in water, but put them in a 5 gallon bucket for a few hours (a mag 5 or an ehiem 1260 in a bucket will quickly exceed 100 degrees at average room temps similar for any ~60watt pump)
Temp wise you don't need to worry unless your getting up over 80, and most coral and fish don't mind even higher temps. You just don't want rapid swings of more than a few degrees.
Set your fan to run at night based on temp also as long as you have an ATO in place evaporative cooling alone can drop the tank several degrees, especially in Montana where you don't have the crazy high humidity or daytime temps to worry about. You could also look at mounting some or all of your pumps external during the summer which will reduce the heat going into your tank by a good amount (in winter though you'll benefit from them all being submerged)
You really don't need a chiller unless your needing to pull the water temp down more then 5 degrees.
I let my tank get up to 82* during the summer months and at that, there is nothing to worry about. My corals and fish are all just fine and I've got over 70 fish in my tank including large tangs, several pygmy angles, cardinals, blennies, goby's, butteryfly fish, wrasses, damsels, cowfish, chromis etc.. All of them thriving. While I could keep it cooler by having my fans come on sooner, I already evaporate over 5G per day and as far as my tanks health, 1 or 2 degrees lower won't make any difference short of using more RODI to compensate for evaporation.
Like you noted, most fish and corals have no issues with temps above 80. Much of our corals and many of our fish come from climates where reef temps regularly hit 82-85* during the warmer months and in some cases, even higher. While running at 82* isn't a real issue, the bigger concern would be large temp swings at night in a smaller system. This is something I don't have to worry about but it would be a concern for others. Fortunately my pumps double as my heaters so a heater is something I've never run on my large system and with my water volume, temps swings are VERY slow.
I used to keep my tank temps at or below 78* and since I raised that level and set my fans to come on at 82, my chiller hasn't turned on in two years or more and I've seen absolutely no ill effects from the increased temp during the summer months. My fish and all my corals thrive. During the winter, my tank runs around 77* on it own.
OP, a couple good small fans or even a single fan blowing across the water in your sump will do wonders for controlling your tank temps. I can drop my 600 gallon system by 1.5* in a couple hours with my two 8" clip on fans from Walmart. I use my Apex to control my fans and it works great.
