My previous mash tun was a 10 gal beverage cooler w/ a kettle screen used as a filter. According to www.hopville.com, I was getting about 70% efficiency. I have only brewed 6 or 7 batches on my new system and I am still working on getting it dialed in. The best efficiency I have gotten so far is a little over 80%.
The main reason I wanted a full false bottom was so I could run my pump as fast as I want and not worry about a stuck sparge. Personally, I don't really care about getting a super high efficiency. If I do, that's a great bonus, but grain is cheap - I don't mind spending 1 or $2 more per batch. I am more concerned about consistency from batch to batch.
And Jaybird, thanks again, man. Hopefully someday I'll post a 'build' thread, but until then, here's what I made: