In case someone is still playing around with IC2 exp.
First of all, I am glad I stumbled upon this forum while looking for vents-only reactors with good EU output. Thank you for sharing this setup, Gon009 !
Especially liking the normal heat vents on the lower corners, surviving because of the component heat vents we have to place anyway.
Since you left three places empty, two single MOX cells (2x4=8 HU to the hull) and an advanced heat exchanger (8 HU from the hull) came to mind. The result is a generation of 1613 instead of 1570 EU/t at the temperature chosen by you (8400).
Went with that setup for a week and thought, there might still be room for improvements. As it turned out dual cells instead of the single and one of the quad cells is indeed possible:
Replace one quad cell and fill the three empty spaces of the original setup with dual cells. Now we are at a stable 1657 EU/t at 84% reactor heat. The best part being: It's symmetrical 
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This is the setup code for IC2 Experimental Reactor planner.
There might still be room for improvement (without going to cooling cells or condensators). But trying to replace another quad by more duals, one of the oc heat vents has to be replaced wisely.