GBADoom 2.6 - DARKEN.wad MAP04 framerate
https://github.com/doomhack/GBADoom
Just a little benchmark of one of my favorite maps from this 25-year old PWAD in the GBA PRBoom port emulated with mGBA. As you can see, it starts off decently. However, it quickly becomes unplayable once it reaches the wide-open area. Also note that savestates must be used, as level saves don't actually save progress in levels, just the ammo + weapons.
In its current state, this port really isn't good for anything except simplistic 1994-style PWADs. Maybe with FastDoom's optimizations, it could at least maintain a double digit framerate.