7.8% is incredible. Based on my experience, I think 1-2% is benchmark.

But really it depends on how widely your service is known, and to what extent it appeals to the mass market. Make either of those variables higher, and you'll get a ton more free users, and quite a few more paying users, but your %age will be worse.

Bottom line: looking at your traffic, I'd focus on getting yourself better known and getting more users, rather than converting the people already coming to your site.