I have the 70 qt. coleman extreme, and I have done 2 5 gal batches in there so far, 1 large and 1 small grain bill, and I have lost maybe 2 deg. over an hour mash, so you will be fine with the 10 gal, and will appreciate the extra space when you want to do a big beer. +1 on the preheating though, either by shooting a little high on your strike temp and letting it drop, or I just fill mine with about 3-4 gallons of hot water straight from the tap (130ish) and let that sit for 20-30 min. while I am getting the rest of my stuff together. Beersmith will even let you put in the temp. of your pre-heated tun and account for that in strike temp. calculations.