In addition to the abov, if you can stretch to the Perc 6i it will give you a bit more performance as it supports SATA NCQ, and it uses a lot less power (you might need to stick in an extra little fan with the Perc 5):
http://blog.peacon.co.uk/bargain-on-dell-perc-6i-raid-controller-direct-from-dell/
Another option, depending on your storage capacity needs, would be to get a decent SSD instead (SF-1200 based for example) which will give IOPS in a completely different league, at the cost of capacity of course.