I have a Janome 6600 so I think I have a 9" throat - I've FMQ'd a huge king-size quilt (full 10' square) on that one. THAT was a chore!
On my prior little machine (Brother CS6000i), largest I did on that one was a twin and that was not much trouble. I think I could have done a double sized quilt but probably not much larger than that...at least not without a lot of work and swearing.