Maybe I've missed something, but I just had a large steam turbine running with two thermal boilers and had very disappointing results. I set it all up, completed with large tungsten steel pipes and all, and gave it a run on 512 B of lava. Everything seemed to work fine but by the time the lava had run out, the generator had only produced a little over 1M EU. So, ~2,000 EU/B.
Thermal Generators are 30,000 EU/B.
It seems better to just run an array of thermal generators instead of pursuing the (albeit, cool) large steam turbine.