i'm using quake1 demo with timedemo demo1 to check fps
Regarding overlay mode: it's a hack currently so it works only in some games and it requires powersdl.library from the link (but it is faster and gaves scaling for free).

For surface you can select scaler mode with aspect and etc.
For speedup i can suggest to set cycles to some const value (60000 here but for slower machine it should be lower).

[ Edited by zukow 25.01.2020 - 10:17 ]