Nothing ventured, nothing gained, so 'tis said, but you will assurely gain in Spring, should you venture then, whereas you may well fail should you venture now.

Dividing plants inevitably damages their feeder roots. These need time to re-establish themselves. Warm-season grasses, like Miscanthus, shut down early, and even transplanting grasses from pot to ground (which they usually barely notice) should be done before mid-October in zone 5.

If you go ahead, act quickly. Divide into large clumps and put them in very large pots or transplant immediately. Keep divisions well watered, and do not feed them. (A bit of compost to make a friable, well-draining soil is okay.)