Migration from SE 4.0 to Online 5.0

[Hmmm. It's possible that this went out with an unfotunate .sig. I cancelled it, and am hoping that it will go away :-) ] Our organization is planning to upgrade the database we are using. We will either upgrade to Informix Online 5.x from 4.00 UH1 SE, or we will switch to a different database vendor. Obviously, the path we choose depends heavily on migration costs. So, the question is, how much is required to change from SE to Online? What problems would we incur? We run Informix on a VAX 6410, with Ultrix 4.0 as our operating system. I am pretty sure that we will need to upgrade our operating system, and chances are that the Vax will be changed as well. Most of our reports are written in 4GL, some in ace, and most of our screens are use sperform. We do have a couple of database systems written entirely in 4GL (screens, reports). We have several c programs, including one monster (from our point of view, anyway :-) whose purpose in life is to reconcile double data-entered tables (compare records in two identical tables, update a flag in one if records are the same, and delete from the other). Thank you for your help, Viktor