As you might already know that we have changed the XSLT compiler with BizTalk Server 2013.
if you are one of our customers who heavily utilizes maps it would be benefit to upgrade to BizTalk Server 2013 or R2.
Here is what we found in BizTalk Server Performance Lab when we compared difference in XSLT Mapping
Scenario: SAP IDOC(POS) to EDI(810) - Single map with extensive logic and schemas and the size of MAPS+Schemas DLL was greater than 6 MB
The following table shows the side by side comparison
BizTalk Server 2010
BizTalk Server 2013
95% processor utilization
63% processor utilization
we also were able to test BizTalk Server 2013 with 500 docs/sec and the CPU utilization reached about 90%
so from above you can see BizTalk Server 2013 and gives you significant performance enhancement with large maps.