After much research the latest version I managed to find version 4165 by David Knight, which is much better than the stock version.
That said, it still is an outdated version.
My question is will there be a newer port, or support, after all those Opendingux handhelds? I find it obscure to keep updating ports for Wii, PSP, but not fresh new devices like rg350.
4165 was the latest version I found back when I had a GCW0, I agree it's better than the stock RG350 firmware version 4077, which crashes when trying to play some of my .paks. I think at least the 4077 should be swapped out for 4165 in the stock cfw.
Here's the David Knight updates in 4165:
Original port by Shin-Nil
Update by David Knight
Changes by David Knight:
* SD card pakfile support (request by alexei_gp)
* Latest OpenBOR engine (Now using SDL2)
* Vastly improved pak file compatibility
* Support for high res pak files (automatically resized)
* Support for 16:9 screen format
* Support for full screen/aspect ratio options
* Menu control improvements (fast scroll, page up/down, jump between header to footer of lists)