Would like to share my lagging issue here: I tried F3 power saving change, Shift+G Renpy rendering change, video driver update, none of them solve the lagging.
And finally, I moved the entire game folder from my HDD to SSD drive, the lagging become much much better. I think the game is asking Hard Drive "task" once in every 3-4 sec(I guess that from the F3 fps window on the top left). It does not sounds to related to video card or rendering etc...
Lagging still there with my game, but much better and now in acceptable range.