The main difference is in the core and memory speed:-
mx440=270mhz core & 400mhz memory
mx440se=250mhz core & 332mhz memory
Here's some benchmark scores for a regular MX440 and a MX440SE tested with a AMD Athlon XP 1700 processor, tested using very high quality settings:-
(results are=mx440se, mx440)
Quake 3:-
800x600x32bit=162,174
1024x768x32bit=122,141
1280x1024x32bit=102,120
Quake 3 2xfsaa:-
800x600x32bit=111,129
Quake 3 4xfsaa:-
800x600x32bit=56,66
Return to castle wolfenstein:-
800x600x32bit=124,140
1024x768x32bit=89,116
1280x1024x32bit=73,100
Serious Sam 2:-
800x600x32bit=84,120
1024x768x32bit=57,84
1280x1024x32bit=39,69
UT2003 flyby (Antalus):-
800x600x32bit=75,86
1024x768x32bit=51,59
1280x1024x32bit=34,40