Sounds good, let me know how you get on with setting t.MaxFPS in the console.
Regarding getting refresh rates, you have a couple of options:
RHIGetAvailableResolutions gets all available resolutions and refresh rates for the monitor in use, including any above the currently set Window’s refresh rate. It also reports the NTSC broadcast rates, such as 29.97, 59.94, and 119.88.
There’s also the FPlatformMisc::GetMaxRefreshRate() that asks for the monitor’s configured maximum. From there, you can compute the VSync internals by incremental divisors, i.e., for a display currently set to 120Hz in Windows the first is /1 for 120Hz, then /2 for 60Hz, then /3 for 40Hz, etc.