I'd sell your current wide, then buy a 5d classic with a 16-35f/2.8L. And I think you're underestimating the 28-135 lens on FF, I prefer it (as do several others) to the 24-105 f4L!!!!!!!! It's lighter, got a better zoom range than the L, so as Ken Rockwell puts it 'unless you spend all your time looking at images at 350%, or you need something to brag about that isn't being skilful, get the 28-135'. It's an awesome, underated lens.
Hope I helped,