Some think it doesn't matter but some think that it does. So if this doesn't matter to you, please ignore this thread and let the rest of us enjoy the research! The only identifying mark so far is that user "Jollywombat" mentioned that his new Surface Pro 2 with the updated 1.9 processors has a Lot Number of 1351. My model the 128 SP2 has the old 1.6 processors and my Lot Number is 1341. Please take a minute to list which model you have and whether or not you have the new updated 1.9 speed processors. This is in reference to the following article. Surface Pro 2.5 i5 4300U 1.9 Ghz 2.5 Ghz - Microsoft Community As an update of 3 pages of thread results it strongly appears that the new 4300u processor starts with Lot 1350 so if you get Lot 1349 or lower you will get the older/original 4200u processor.