Brad that IR is at TSC has a couple of problems that we simply can't overlook because too many people ask about compressors here. First they are just flat out lying about that 18+ CFM rating which is just unrealistic for that single stage pump/motor combo and recently some places have started rating it at a more believable 15+ CFM.
Same IR compressor that TSC sells but a full time compressor outfit rates it more realistically
Second they have a terrible reliability record and are notorious for burning out motors, we had a thread here not long ago with four owners of the darn things complaining about burned out motor problems in just that one thread! The IR at TSC is not an industrial USA built Ingersol Rand that the IR name is built on it is a Chinese import and unfortunately has earned a not so good track record. Also your example of hot air from a 20 gallon tank vs an 80 gallon may be valid but not so much for the 60 vs 80 with the differences being slight and even the little tank may not be as bad as it might seem. Because of space limitations we built quite a few high CFM small tank combinations for service trucks, some as much as 40 CFM with a 25-30 gallon "bumper" tank to save space (the rear bumper served double duty as a very heavy walled tank) plus various other combos of small tanks with high CFM and they did get hot but only under very high demand.
Honestly the heat difference between a 60 vs 80 gallon is going to be negligible for the same reason over-all air (in CFM) remains the same, the same amount of air enters the tank carrying the same amount of latent energy (heat) with only a small difference in cooling due to slightly more surface area of the tank, the amount of air flow through the tank is the same regardless. You are correct in your thinking and the extra cooling effect is real but just like the other advantages, energy savings and pump/motor life, the advantages are slight and not worth passing up better performance in the form of CFM and/or better quality. I have in the past harped a great deal on tank size because it is such a mis-understood factor when selecting a compressor. I in no way mean to say that a bigger tank is not better and usually it is but not always and not for the reasons most seem to think. It is useful in that it saves both on power consumption and pump motor/life due to fewer high torque start cycles, this can be substantial over the life of the compressor but negligible in the short term. Making a blanket statement that the 60 vs 80 gallon makes little or no difference is because 90% or better of the compressors being discussed here are in the 10 to 15 CFM range and in that class of compressor 60 vs 80 gallons simply will make little or no noticeable difference.
The point is that many times, far too many times, someone will pass up higher performance just to get a bigger tank and that clearly is a mistake! The compressors being considered in this thread are very good examples of the 60 vs 80 gallon dilemma that comes up so often and in this case the difference between a 60 gallon vs an 80 gallon really is very slight. As CFM increases the size of the tank becomes a more important consideration but up to about 16 to 18 CFM or so 60 vs 80 gallons really is going to be a toss-up. CFM rating, Duty cycle, pump type and construction quality plus the motor AMP rating (true rating) and service factor are all more important considerations when selecting between a compressor with a 60 gallon tank vs an 80 gallon when choosing a compressor of the size being discussed here.
EDIT: Danged if I didn't do it again!!
He clearly said the TWO stage IR and I took it as the single stage!
I think maybe there must be something wrong with my coffee!