I recently asked the question on the SQL Server Forum about the difference between the build numbers. Build numbers in the 30xx range are for GDR patches while build numbers in the 31xx range are for the QFE patches. Here's a reply from Michelle Alexander on the SQL Server product team in regards to my question on the difference between build numbers:
"Yes it is a little confusing but the good news is that installer will make sure that you do the right thing and block you from installing an invalid fix.
Let me attempt to describe how this work. From a customer point of view there are two possible trains you can be on for fixes.
The first is the GDR train where the minimal number of fixes that meet a really high bar in terms of severity and wide impact. They are the lower build number range.
The second is a general QFE train where general fixes that are requested by customers through CSS are added. This has a higher build number range.
Since our QFE's/GDR's are always cumlative then if you need a specific fix that is in the QFE train you always pick up your fix from the QFE train or range of builds. The QFE tree always includes all GDR and QFE fixes.
If you install a GDR and you need subsequent GDR then you pickup you fixes from the GDR train. If you are on a GDR and need a subsequent QFE then you would pick up your fix from the QFE train and stay on the QFE train.
Hopefully I did not make that more confusing
I hope this helps explain the difference in build numbers because I know I wasn't the only one that was confused when I saw the latest 2 KB articles from MS (934458 and 934459).