Efficient BOffs actually do stack. I've tested my 4 Saurians and came to the same results as in the spreadsheet. It also showed me that an additional fifth Saurian just adds a single point to two of the four power levels. I'll better keep my TSS III Tac.
I'm using this spreadsheet for 2 weeks now and it helped me saving al lot of skill points. I was wondering that no one else has posted in this thread when I rediscovered it yesterday. Seems like it has finally gotten the attention that it deserves.