3 ugly sisters
Buckshot,
OEB/C/D are know affectionately as the "3 ugly sisters" partly because they had a host of "differences" when they entered service with Q. A lot of money was spent aligning them with the rest of the fleet.
As for performance, I seem to remember the GEs performing pretty well because:
1. GE engines are much much lighter than the Rolls (2 spool vs. 3)
2. Haven't been on the 400 for a while but seem to remember the climb thrust derate tapering out at a lower altitude than on the Rolls.
Above about 20 000ft there was no noticeable difference between the GE and Rolls powered versions. The Rolls had a few advantages over the GE in other areas; they operate better off opt. altitude and they carry ice better (so I'm told!).
WG