Hello August,
you won't be able to compare/evaluate the effort for su25 2c before the upgrade. Because first you need the new content of usobx and usobt, which you get by upgrading the system!
Only if you have already an upgraded system, yopu could compare the effort.
But starting in 46x with target to an acutalk release (7.31/7.40) will bring you almost all of your roles in 2c....that is , what the expirience shows.
So take your time for adapting your roles and especially for testing them together with tthe new funcitonality.
b.rgds Bernhard.