Ace, ok, don't hold me to an exact number now. :-D
Its not that she will leave entirely but more that a virgin will go back to where the cluster is and you have to keep dealing with re-housing them, which is fine unless the swarm was situated 20' up in a tree.
I prefer to cage queens for that reason.
You could vac the swarm, place the branch in a box, set up a catch box adjacent to the swarm...
Let me mention this, based on my experience, queens will generally hold tight to where the cluster is, so it is usually prudent to physically move her or the entire branch. She usually will not leave the cluster on her own.
A catch box with a brood frame is an entire story all together and she likely will enter that, but who has a brood frame on hand unless the swarm is in their own bee yard?
As I mentioned, I prefer to shake most swarms unless they are 20' up on a branch I can cut and lower to the ground.
I enjoy shaking them and watching them orient, besides that I always look for the queen and I can't do that unless I shake them.
You could also shake them into the set up and have an excluder on so she cannot leave. This is a common enough practice as well.
One clarification: I previously mis spoke when I said caging queens could calm a swarm's urge to leave the new set up. That is not the case. They will try and leave regardless but if there is only one queen and she is caged they have no choice but to go right back into the set up. Something I routinely witness.