Two observations:

Sbfactorer does not seem to be based on the v23.4 gimps sources. Stage 2 was rewritten two months ago to use more memory if it can, use fewer multiplies, and to be more efficient in low memory situations.

There was a bug fixed where sub-optimal bounds where picked for the P4. An Athlon and P4 should pick very close or identical bounds.

Don't expect great improvements, but every little bit helps.