Viper Lair posted a review on the Mushkin HP2-6400 4GB Memory Kit

The Mushkin HP2-6400 kit performed very well in our tests today and for the most part, performed a little better than the Corsair 6400Pro which did suffer from a 2GB capacity disadvantage. While the difference in performance between 2GB and 4GB isn't terribly large in day-to-day applications, if you're in a specialized environment, the extra ram will play dividends. This is very clear in our Photoshop and DVD tests.

Mushkin HP2-6400 4GB Memory Kit Review