Try running OpenEmu. OpenEmu has Syphon support built in.
There are a lot of issues here.
1: video games don’t run at 60hz like your monitor does, but typically 29.97.
2: Game emulators don’t always do the right things to compensate for the frame rate discrepancy, so it can be hit or miss in terms of frame rate just on its own (I know, seems weird but its the case sometimes still just due to phasing)
3: Everything Tom said about Syphon Recorder being meant for realtime, on demand, just in time frame arrival means it has a VERY hard time meeting the FPS you desire, even if the host app runs at a smooth 60Hz, frames don’t arrive at *exactly* the same time, there is, for lack of a better word, ‘clock drift’.
Try OpenEmu. I believe it has native recording, and if that doesnt suffice, try its native Syphon support, see if that helps.
Thanks for taking the time to write that up.