Looking at Vista's I/O Performance
 

Originally, we set out to compare various RAID and AHCI SATA controllers and
what kind of performance we can expect with Vista. But problems during
testing lead us elsewhere - this article. These preliminary testing clearly
shows that kind of comparison is just not possible right now - something is
still definitely broken with Vista's I/O performance.

http://www.tech-hounds.com/article29/ArticlesPage1.html