I've yet to read about any pre-2B5 board that works reliably (i.e. also tested successfully with Linux, because that works harder on the memory than MorphOS) with 2× 1 GiB, and even with 2B5 it's hit or miss. Theoretically
, all boards from 2B1 on should work with 2× 1 GiB, because that's what the official mainboard specs
here is succesfull 2GB with rev 2B1 2GB on Pegasos 2 rev 2B1
And as I gave him some advices when he installed and tested MintPPC it looks that it works with linux.
But this is the only Pegasos 2B1 revision with 2GB I know about.
Pegasos II 1.33GHz, AmigaOne X1000, Powermac G5 Quad, iMac G5, Powerbook G4 and Z10PE-D16 WS
MorphOS, AmigaOS, Debian, Ubuntu, OSX, NetBSD, Win7