The cab layout on the 4840 will be a little nicer than the 5488 but overall I much prefer the 88 series cab to the Sound Gaurd cab and even if the doors swing the wrong way on the 5488 they are still easier to get into than the Deere. 

Something I haven't seen mentioned yet is fuel use, most reports I've heard from 4840s is upwards of 10 gph when using them hard and I have yet to see our 5488 use over 6 gph, and that is pulling a silage chopper or 11 shank disk chisel.  If the 4840 is going to use an average of 2 gph more to run that's $6/hour with current fuel cost. 

Also the 5488 is a little smaller frame than the 4840, that's why it won't ride as nice but in tight quarters the 5488 will handle almost as good as a 1066.