Topic on Talk:Sonic Adventure 2
The game speed is tied to 60hz. Setting to 60hz mode is the best option IMO. If you have a VRR Monitor for example, then it shouldn't be much of a problem since it will be the same as being a 60hz native monitor.
Whether this still lets you use something like ULMB I don't know, I don't have a VRR Mon. Backlight strobing at 60hz doesn't bother me much though considering I still use a CRT television for old low res consoles and 480i consoles (Which flickers way more than 240p/480p60)