Dev. Tools for Informix based apps

We are going to develop a medium sized (200 seats) in house application. It will cover the complete document management, logistics and communication functions requiered. The server side is Informix 7.22 on a Unix machine the clients are running NT 4.0. The new app should have a GUI, at the time we have a terminal based interface. First approach was to use "low level" tools such as Borland Delphi. But the estimated times to develop a reliable product with these tools seems to become too long and support will probably become a nightmare ... Now i am looking into Unify/Vision and Magic 8. Does anyone have experience with these tools ? What other tools are available ? Thanks for help Peter