Who's using what?

I am trying to research the Informix database market in an effort to determine which versions of OnLine (5.x, 6.x, 7.x) are most prevalent in the user base. We are considering writing a developer's tool and the different capabilities (particularly between 5.x and 6.x) would effect our design in a many ways. We would like to focus our energies where the majority of the customer's are. Are there still significant numbers of people using 5.x? Are they likely to migrate in the next 6-9 months? Thanks for your help. charlie peck charliep@earlham.edu