However, in terms of low frequency extension, 2 500s wouldn't have the same low-end capability as 2 600s (or 800s), and I do really enjoy the low-end of the 600, and imagine I'll enjoy the lower end of the 800 even more. I suppose if I turn out to be completely wrong I can send it back... there's always that option.
I think that is why I prefered the PB13 to the 600, that little bit of lower extension.