Hey,
I´m wondering about the same things concerning my PRS Tremonti (which has a tremolo, too).
I need a 51mm spacing (have just measured it) so I have to choose between the "classic" 49mm and 53mm
(I guess that it won´t affect the sound anyway)
Think you will need the short leg plate because your PRS hasn´t got this thick, "Les Paulish" body (mine has, so I´m gonna take the long leg).
If you wanna make sure that it really fits, you have to detune the strings and dismount the screws of the humbucker-ring and take a look at your stock pickups.
My "plan" was to take a cover (only optical reasons !) for the bridge Pu (leaving the neck position without a cover)
But now I´m afraid that the cover will not fit into the ring of my PRS (have just measured it and it lacks of 3mm space....the ring is too narrow at the inner side).