I've been playing with BigReactors extensively on my Monster server, so I'll give you my points:
- Liquid Ender is the top coolant, bar none.
- Making a reactor taller rather than wider is better. With liquid coolant, you only need source blocks along the top. So a 5x5x5 reactor needs the same ender as a 5x5x20.
- Temperature is the biggest factor in efficiency. Keeping your heat below 1000* is my personal preference, because at 1000* the fuel penalty is only 10%, but as you approach 2000*, the penalty goes up to 66%.
- The ComputerCraft controls are impressive. HERE - http://pastebin.com/JCa6CmhL - is my own custom script. It displays vitals to a connected monitor, and dynamically controls the reactor rods to maintain a running temperature of ~820*.
I produce about 1800RF (180MJ)/t at the running temp. of my current setup = 8-rods, 7W x 11L x 15H. That's with rods at about 81% removed. During a cold start (computer sets rods to all in) I've seen numbers as high as 8500RF (850MJ)/t.