4GB is barely enough just to run mountain lion itself. Upgrade to 8GB and it should run much faster.
I use a macbook pro with vmfusion 5.0.3 & win7, 2008r2, & ubuntu all work like champs. Since you can't reuse the 2 2g cards, think about upgrading to 16g rather than 8. You won't be sorry.
Also, have you checked your drive space ? Since I use ssd's I used 256g drives for the raid array so I am mindful of what I keep on those drives.