the 250 size is popular, we did a "spec" class race on Jan 3rd (actually did 10 races, made a day of it :) )
Spec class is 250 sized, 2300 kv motors max, 5" prop , 4 motors max (you can run 3 as a tricopter) and 3S lipo
very even playing field , in the final around a 400 meter track for 5...