Hi there,
I would suggest it depends about your situation, the most important step is the overhead, but if you use vpn policies aswell a too big overhead might also not something what you want.
I have been testing this for the fun, but I have seen some crazy latency issues when a link suddenly gets alot higher bandwith I guess best is to recommend, is to create a SQM policy for each individual connection or device group with in mind that you use a vpn more as a static connection and not to use it dynamicaly to enable/disable, it seems sqm is sensitive on this.
as your example, I think you should be fine, I always make a small calculation and substract 8% from each device group… for example my TV I give the highest priority, my tv is isolated on its own network, and then with the next group my lan I substract it again from my tv data, this way I always create some overhead and also some kind of priority tree.