Epic, I am using Iridium Neutron Reflectors, as shown in the uranium build that I posted. My efficiency values come from the reactor planner online, I wasn't aware of the thorium/plutonium problems with the online planner. However, you can see the eu/t output of individual cells on the planner, and I've tested to make sure it's correct (it is) and the 3 plutonium cells in the build that I posted output 130, 90 and 90 eu/t. The thorium is there to make the plutonium pulse more, so I'm not really worried about its output. Also it's easy to obtain, much easier than plutonium.
Since posting this, I've found a better thorium/plutonium design. The 2 plutonium cells output 170eu/t each. Therefore it's more efficient and has a higher output, but uses more thorium.
I didn't design it, and the person who showed me didn't either. So I don't know who to credit.