Now that's weird Wolfe - postie delivered my motor/esc for my Beaver today! Sadly it's not a GWS one, though.
I use 800 or 1000 3s in all my smaller GWS warbirds except the Spitfire which uses a 1250 3s, same as my larger GWS warbirds. Picomoth uses 450 2s. I can remember the first one I built - used a 150 6 cell Nicad. Good for about 90 seconds if you were really lucky!
The biggest batteries I have are 2200 3s.
And the best duration - I flew an E-starter deliberately looking for endurance - can't honestly remember what size battery but it was up for so long that I got a crick in my neck as well as being hugely bored. It was at 25 minutes that I decided I'd be better lying on my back in the grass. I have no idea exactly when it was I went to sleep but it was at 35 minutes that I woke up again
and it took me quite some time to find the wreckage!