Hi there. There is my variation of "spit on the efficiency" reactor:
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Reactor: Mark I-O EE
Chambers: 6
External cooling: 20, by water
Active EU/t: 140 EU/t
Total EU: 28 000 000 EU
Efficiency: 1.00 
Effective EU/t: 140 EU/t
Cooling cells: 28
http://www.talonfiremage.pwp.blueyonder.co.uk/reactorplanner…1501521s1r11r10