I have my big B gelding and small Shetland mare in an approx. 80-100 ft. corral, and they have a great time racing and playing. What is the total room you have available? Rather than two equal size areas, perhaps you could make one larger.
As for fencing, we have one corral in 4 ft. no-climb and the other in 4 ft. welded wire, each with hotwire at top and at knee height. I would never use either, especially the welded wire, without electric to keep them off the fence. With electric, you could also use field fencing, but I'd probably add a third hotwire for safety. Without electric, they will destroy any of these type fences in no time.
My 38" gelding showed me that he can hop over the 4 ft. fence from a standstill, no sweat. Lucky for us, he stays in by choice, but grain is locked safely away.