Top's guns run on a different type of gear box that is meant for cycling many bb's before braking down. The only problem with the gear box is that you have to be a gear head or know some one who is because the gear box takes a little more maintenance than your average gear box. I thought about buying a M60 also and if you Google search the top models you will find a pacific island (Woot I have family that plays this sport) forum that has a HUGE page on this, that might help you. I'll try to find the link for you.
Ninja Edit: Well I found it for you, here you go
http://www.airsoftpacific.com/content.php?page=21