L310A678-->3.7ghz@Vcore=1.55
L310A847-->3.7ghz@Vcore=1.52
L310A744 @ 3.6GHz@Vcore=1.55
L311A763 -->3.5ghz@Vcore=1.62
L309A614-->3.5ghz@Vcore=1.58
L310A744-->3.5ghz@Vcore=1.52
L310A579-->3.48ghz@Vcore=1.52
3312A486-->3.48ghz@Vcore=1.52
3317A235-->3.42ghz@Vcore=1.55
3312A431-->3.42ghz@Vcore=1.49
3312A296-->3.36ghz@Vcore=1.52
L309A586-->3.3ghz@Vcore=1.5
L310A742-->3.3ghz@Vcore=1.5
L311A867-->3.36ghz@Vcore=1.58
L310A598-->3.26ghz@Vcore=1.5
This is the list I saved long time ago when I first bought my chip and users on Anandtech reported their steppings to see which overclocked better.
Look at your chip to determine where it is from:
1st letter or digit=plant code
0=San Jose,Costa Rica
3=Costa Rica
1=Cavite,Philippines
R=Manila,Philippines
7=Philippines
9=Penang,Malaysia
Q=Malaysia
L=Malaysia
8=Leixlip,Ireland
Y=Leixlip,Ireland
6=Chandler,Arizona
Example: Q320A269
Q=plant (Malaysia)
2nd digit=Year of production (2003)
3rd & 4th digits=week (20th week )
(A269)=some kind of traceability number
As you can tell, Malaysia chips were consistently best overclockers. Not sure if this holds true for current 3.0ghz northwoods.