formation crashing video on our club site www.rcflyers.net
we also formate at 180mph when running the quickies together..
formation prophang with 3 or more up at once
but it's also quite possible to get ww1 bipes to fly together quite happily, getting them staying together either needs two good pilots talking, or one very good pilot to follow the first ok pilot

i've only ever seen formation aerobatics once, it was by two TOP pilots, but it was nothing compared to the real deal.