Oh, forwarders are basically separate copies of the [RetroArch + choice of core] emulator containing one rom, stripped of everything except for basic drop down menu, and wrapped up in a pretty banner & icon to look at in HOME Menu. It's kinda like the difference having a collection of books on a bookshelf versus Amazon Kindle. Same stories; different reading experience/medium.
The performance of RetroArch (Genesis Plus GX) standalone emulator versus the NSUI injection (RetroArch Genesis Plux GX forwarder) are identical:
Phantasy Star runs too slowly on the o3DSXL when FM audio is enabled.
The next best idea I can think of is to emulate the game on desktop and stream the video feed to the o3DSXL through
TinyVNC,
PinBox, or
3DSControllerPlus and listen the audio with a bluetooth headphones. This is how some are able to play GameCube, Wii, Switch, etc. games on the 2DS/3DS. Granted, there might input lag or washed out coloration to image.
For the New 3DS models, Genesis Plus GX is probably the generally more accurate of the two compared to PicoDrive when it comes to GEN/MD games. PicoDrive should work fine for the casual gamer who's not super picky with minor frame drops or notice the minor graphical bugs here and there.
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EDIT - I will revisit the
Sega 3D Collection injection idea for the last attempt at perfecta. If that
Fantasy II is pixel perfect in the original CIA, I'll hex compare and try to look for a pattern to how the SMS rom in the collection differ from scene dumps.