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.
I took the time to visit the website and he says, 7.8% is the ratio paid/free of the current accounts they have, but there is a but, they are not offering a free lifetime account. So, this is why the ratio is high as the people who just wanted to try will get their account removed after 30 days.
In fact, this ratio may only increase with the time for such offers as the number of paid customers will increase over time but the number of new signups may start to plateau.
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.