It is probably best to wait until the plants begin to leaf out in spring. When I move them then they suffer no setbacks.

It might be a bit cold in your greenhouse to get reliable rooting over the winter, by mid fall it can be hard to find fresh rapidly growing shoots. You could try to layer some branches now. Bury some fresh stems just below the surface and put a brick on them to anchor them. These have a good chance of taking and can be seperated when you move the main plants.

For what it is worth in the future, mid August thru mid September is a great time to take cuttings - at least here in New Jersey. You could even look further ahead and layer stems in June when plants are in their fastest growth. They can then either be left for the following spring or removed later in summer and put in the their final destination.

I would let them bloom and when spent, cut back by a third. Then as Wardaa says, dig up and move in spring - splitting those big clumps into several smaller perennials along the way.

I am rooting S. microphylla cuttings unheated & outdoors in my backyard now. It's not ideal, but it is easy and worked last winter. I would agree through that Wardaa's advice will give you more vigorous growth and a higher success rate. But if you are going to prune and you have the space & time, it's pretty cheap to stick the pruned stems in moist vermiculite and a recycled container and see what happens.

I'm in central North Carolina, and we are about to get our first really cold weather. From Sunday night to Thursday morning, expect lows in the upper teens. This is not a good time to transplant even hardy sages.