I don't know of any workarounds other than, perhaps, trying to obtain a different version of the PGA Tour Golf rom. Megadrive/Genesis emulation has been pretty good on the Letcool, in my experience, so hopefully a different dump of the same game or one for a different country may work better for you, but that's just a shot in the dark.
As for firmware, the lsd_blottr (that russian guy) custom 2.2 firmware is great in my opinion. You can try the 3.1 Defender firmware provided by 1wiierdguy but several people, including myself, found that it moved their screen off-center after a system repower so don't be surprised if the same happens to you. Flahing back to lsd_blotter's custom firmware should correct this issue if you encounter it. Someone reported that the 3.1 firmware showed improved emulation performace, but I didn't find any evidence of this in my brief testing of SNES games. Perhaps I just tested the wrong games or the wrong system.
I would suggest sitting tight with the firmware you have for now. Hopfuelly someone will continue to develop firmware with improved performace for this device.