Mark II
140 EU/t running, 97.56 average
2.33 eff
http://www.talonfiremage.pwp.blueyonder.co.uk/reactorplanner…1f21s1r14lflr10
The Bottom right HD can be removed and replaced with whatever you want for virtually no difference in the reactor.
If you have a very severe need for power it can safely be replaced by a uranium cell for 10 more EU/t and reduced efficiency, and a 20 minute longer cooldown.