Usually, that leggy, anemic looking growth is the result of insufficient light combined with enough warmth to encourage the plants to emerge from dormancy. And yes, it can be cut back.

I winter clematis in containers outdoors all year round, so they can certainly take cold temperatures. You can probably bring them out now as long as you do so gradually - an abrupt shift from moderate, inside garage temps to colder outdoor temps should be avoided. I'd suggest bring them outside during the day and return to the garage at night while still cold, gradually extending that process to them remaining outdoors around the clock. If you can time this to coincide with time to plant, even better :-)

For the last two winters, this winter being the coldest of the two here in middle TN, wind chill down below 0 a couple times. I have left out on my west facing front porch with no protection whatso ever three large potted clematis that froze solid. I know I was a bad clematis mommy for doing that but no ill effects either year. I pruned them all about 2 weeks ago and now I have small buds and new growth buds coming up from the dirt. These are four year old clematis, Asao, Romona, Jaskmanii. The large pots are probably close to 15 gal size. I would have to move the pots with a two wheel dolly. Clematis are very harty root plants.

I would think in your zone you could do as they say and gently harden them off with no problems. Expose them to bright shade for 2 days, then a little morning sun for 2 more, etc. Should be no problem.