As others have alluded, you'll be able to program your new VS pump with more then one schedule, and each schedule can have its own speed. You'll determine the optimum RPM setting for your vac, and then create a "cleaner" schedule at that RPM. And that setting will likely be much lower than the new pump's top speed.
My pump will run at 3500 RPM, but I only need 2200 for my vac, which runs 1.5 hours a day. The rest of the time, my pump runs at 1500 RPM (the optimum speed for my saltwater chlorine generator). But...
I couldn't find an optimum speed to run my vac that also kept my skimmer working well. Sounds like you've already discovered that vacs are "suction hogs." So I bolted an actuator onto the valve that controls the flow between skimmer and vac. When it's vac time, the actuator moves to favor the vac, and then moves back to apply 100% of the suction to the skimmers. Now both functions work really well, because they no longer have to compete for the pump.
Plus, I had a concern about the safety aspect of a suction-side vac. It is, after all, an easily accessible suction port running around the pool. I don't trust my rambunctious ones to leave my vac alone, so I schedule my vac to run only when no one uses the pool (very early in the AM). The rest of the time, it's dead, and 100% safe.
The caveat to this setup is the scheduling control. While most VS pumps can schedule themselves, not all can schedule something else (like an automated valve). I have an EasyTouch pool automation controller that handles all that. But there are much simpler and cheaper solutions if you want to pursue something similar. Either some sort of accessory timer, or a VS pump that is capable of controlling external devices. Something to consider when selecting the brand and model of your new pump.
