IMO, Fan #1: pwm 140mm, Fan #2 pwm 140mm, and a 140mm rear exhaust. All connected to PWM mobo headers. No top fan, no side, imo. That's what I'm running on my Arc Midi at the moment, with all three case fans running under 800rpm and temps are fine.
@doyll: nice fans =) I really like Thermalright's 140mms. If you ever get the itch for new ones, I highly recommend the TY-141. Much improved over the TY-140, imo, and the best of their 140mm lineup.