Not sure about the Pi, but the Pandora which has similar ARM class of hardware can run Quake 3 at 25-30+ fps in 800*480 resolution. The GPU of the Pi may be more powerful while its CPU is weaker.
The competition rules said at least 20 fps, which seems playable.
Re:Quake III bounty: we have a winner
by TheCraiggers on Monday March 31, 2014 @10:41AM
(#7501717)
I used to run Doom 2 on my 386sx. Doom 2 required a math co-processor, which the sx didn't have, so I had to use a TSR which emulated one, slowing my CPU down even more. It probably ran at 1-2 FPS, but it was "playable" enough for me to spend countless hours playing it. Ahhh, memories...
So yeah, 20 FPS is definitely what I would call playable. ;)
Doom (or Doom 2 which had basically the same engine with just bugfixes and support for Doom 2 entities) didn't actually need an FPU. Even 386DX's or 486SX's had no FPU so no games from the pre-1995 era really depended on it.
I remember Falcon 3.0 and perhaps some other simulation games having support for FPU for those few who had one however...
Someone ported Quake 3 to ARMv6 Symbian smartphones in 2008 [0]. I remember running this on a Nokia E90 Communicator and the framerate was over 15fps most of the time.
[0] http://koti.mbnet.fi/hinkka/Download.html