I use 12g sliders those are about equal to 10g rollers on low end. and equal to 14g rollers on top end. Sliders give you about a 2g difference on both ends.
You can go down to 11g sliders without losing top end. Here is a vid I found a while back that lets you see the difference.
The best bang for your buck would be a cam upgrade. Cheap and easy to do.
http://youtu.be/yxcQGmT8EJc
I found this video a while back...