The 850's probably don't need to run as "large" - their -3dB point is 36Hz, which is actually a little higher than my Studio/60's -3dB point (I've got my crossover set at 60Hz, by the way). I'd suggest running the 850's as small with either a 40Hz or even a 60Hz crossover. This will let the 850's pass off the lowest frequencies to the sub while still keeping in the mix in the regions where it is still relatively flat.