Currently I am testing applications moved from 2003 server to 2012, what do I need to focus on in my testing? I was thinking focusing on ISS & Net version (since these both are changed between 2003 & 2012) but what else do I need to focus on? My applications are mixed between .net applications, web http applications, and client base (just backend batching) applications

of course the objective of the test is to see there is no performance degradations (comparing results from the previous load test done on 2003 servers and the new results on 2012), but I want to make sure I am covering all "important" areas, so I know ISS & .Net, what else?