What are your needs. I made the upgrade for full frame for two reasons.
1. Cleaner results at higher ISO's (most bodies do have better results for a fraction of the price now)
2. Ability to shoot as wide as possible (for car rig photography).
The problem is, I could tell you that my 1D is even better and its the best thing ever invented, without you trying any of them, no one can tell you any different.
Before setting aside that you NEED full frame, have a look at what you shoot mostly or what you enjoy shooting more, post that up and also some sort of budget.
If you enjoy loads of scenery, full frame might be better for you but on UWA, watch out for distortions. If its more sports or wildlife, a crop body (APS-C/APS-H etc) size might be better giving you more reach.