I have done maybe 200 brews in a 44 l esky which is actually full once Promash thinks it has 39 l in it, due to the old hollow lid thing. Standard batch size is 44 l, starting gravity anywhere from 1.030 to 1.075. The esky size works well for those double batches, as it is reasonably full and so holds temp very well. Sparging is easy, I do both fly and batch. Due the slighly limited space batch sparging usually takes a mash out plus two batches. But for mostly double, and the occasional single batch that is a perfect esky size.