Today I have tried if upgrading to the latest Intel C++ compiler would improve performance.
I had to install Visual Studio 2010 first - wow, talk about bloat.. Installing literally took hours with multiple reboots, and it required 4 GB of harddisk space. Then I installed the latest Intel compiler (13), also over 1 GB.
The good news: I got my code building within minutes (just had to configure some directories), and the binary that came out is a lot smaller than with the compiler version I was using so far (10.1).
The bad news? Performance dropped to 75% of that with 10.1.

And Visual Studio 2010 is so slow that it often completely blocked my system for over a minute if I just clicked on something.
I also tried the Microsoft compiler in Visual Studio 2010: Performance is less than 40% of that of the Intel 10.1 version.
Result: Today was a lost day, I'll restore the backup that I made in advance and will continue developing on version 10.1.