I went to actively cooled with my setup, 7x7x7 reactor with 5 cores. One mistake i made in the past and another person on the server set me straight on, is water consumption. Once you have the turbine going, it will produce enough water to run the reactor, so its basically closed loop. My mistake in the past...I was using fluiducts between the turbine and reactor, fluidcuts could not keep up with the water demand. I use tesseracts now and have no problem. I used 4 aqueous accumulators to start the whole deal, again with tesseracts to feed the water into the reactor. Once the turbine was up and running, i disconnected the tesseract to the accumulators to test and had no issue with the water.
As far as power, i cannot remember the size of my turbine, im willing to bet not efficient as i just built it for shits and giggles. But I was just trying to get decent power for as little as yellorium i could use. So some numbers off the top of my head, turbine is running at 1800 RPM, 17,800 RF/t, 60/72 blades i believe, my reactor cores are turned way down, 3 are set to 70% and 2 are 80%, i use between .04 and .06 mB/t of yellorium. I can get some screenshots later if really needed, but im willing to be you are having same water issues as I was at one time.