It's more a question of size rather than actual material :-) SAC grows into a BIG vine and can quite easily outgrow a standard sized arbor. Mine was trained initially on a 6'x8' recycled metal panel (a wrought iron screen from an old theater) but that only provided a beginning backdrop for its early season growth. By the time it reached flowering season, it had grown well beyond the confines of the panel and into any adjacent support system - in my case, along a fence and into several large shrubs and an apple tree.

While I do prune back new clematis hard for the first couple of seasons in the ground, I don't do it until after their flowering period or until the typical clematis pruning period......late winter/early spring. Not during the standard growing season. I've not found that waiting until the end (or the beginning, depending on your perspective or location) of the growing season for any hard pruning impedes proper root development.

This particular species doesn't need the babying others do, I think. I would trim it in March in our zone and let it go - it's a strong grower. Near Chicago, mine get perhaps 12' tall, but simply grow up, then over their trellises. Assuming your metal trellis is 6' x 2-3', you'll have a nice ice-cream-cone-shaped bloom in August.

Sounds good. That's what I needed to know. I'll start a new post, I have questions about arbors.

It may be a difference in locations, but a SAC here would outgrow a trellis of that size halfway through its first season.....it ate up my 8' wide trellis by June and quickly progressed on to other objects to conquer :-) My vine had no trouble extending 30 feet in a single season and in multiple directions.

It's BIG.....plan accordingly.

Hmmmm....wondering if I can grow this one on my garage face, over the door, like the popular Montana pic that I think most everyone has seen....I would love to do this, but I've always wondered about the appearance over the winter months, probably wouldn't make my garage very attractive????

In zone 6 I always cut mine down in the fall practically to the ground and that would preclude the winter mess. It then grows about 12 feet every year.
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At one end of the arbor is where I have a 3rd year Emperor I Japanese Maple. It's maybe 8 feet in height, not a large specimen, but established. Do I need to be concerned for any reason with S.A. growing into the tree???

Based on my experience, I'd say you have reason to be concerned. It depends on the size of the arbor and how the vine is trained to grow on it, but if the distance is not great and when the vine is mature, it could rather easily encroach on the tree.

Just for comparison, I grow 3 SAC - one I prune to the ground each year and I estimate it gets about 10+' in length. The other 2 I prune quite high so they leap over a fence, so they don't quite count.

Our shorter growing season will limit its growth, I think.