I think it really varies for many based on my experiences. You guys are doing well with 6%, but there are variables that can impact conversions. For example a 1000 visitors from Google search keywords might convert very differently than 1000 visitors from adsense.
I tend to look it from the perspective of not what other's conversions are but improving my own. (a) Can you improve your conversion percentage - a/b test variables related to the purchase process (b) Can you increase the number of visitors while maintaining or improving your current conversion percentage. Focusing on that will impact your bottom line versus comparing to others, but ... 6% is very good
See this thread for more - Good Conversion Rate