Operational ATC staff have had no input in the FR process. It's all been done by BAA computers, and our management, who have never worked Gatwicks runways (or anywhere else thats busy come to think of it!?)
The theory is that Medium a/c and above vacate at FR (doing a minimum of 60kts) and cross 08L/26R without stopping, onto taxiway Juliet, thereby reducing time on runway by maintaining a high speed, so yes, FR is probably "preferred".
If a/c can promise to make the first, then do it by all means, the problem exists when you try it, miss, and roll past to FR.
I've noticed some RJ and BA 146's roll to FR 'cause thats what the AIP now says!!
Gatwick ATCO's know how a/c and airlines perform on landing, and choose the gap size and traffic order based on that. The AIP, thanks to our management, have over regulated the process.
In answer to your question; paper-pushers made the rules without consultation, and if you are confident to make E, then do it! Otherwise, land long or fast and whip off at FR (60kts remember!!)
Good luck.;-)