biggest I've gone to date is 0.5.

The issue isn't really how large a nozzle can you use. But how fast can the printer cool the bead.

I can't see 0.6 being a problem, and you might get away with 0.8.
But you will soon hit the law of dimishing returns.
Ie: because the most important factor is to cool the bead and get it to set as fast as possible, before it deforms under it's own weight.
The bigger the nozzle - the slower you'll need to print.

Unless you add a couple of turbofans and second print area cooler, then 0.6 and maybe, 0.8 is probably your limit. And 0.8 will have to be printed pretty slow.