The Vokey generates more spin because of the grooves and the face.  I had the same experience between an Eye 2 PW (48.5) and a 48-06 Vokey.   You don't need both (same analogy would apply to carrying a 5 wood and a hybrid with the same loft).

It depends on what your preference is for PW usage.  If you use it for long pitches or full swing shots, the set PW is better. 

I don't take too many full swing shots with my Vokeys.  I carry an AP1 PW,  Spin Milled c-c 50-08 (bent to 49 and shortened to 35.25"; swingweight comes out to the same as a 48-06) and 54-14 (bent to 53), and SM4 60-10 (bent to 59). 

I've had the same experience between cavity back game improvement clubs and the traditional style (blade style) wedges. You show about a full club distance so keeping both won't hurt. Paul G. makes a good point to use them for two different purposes. Use the Vokey for finesse and the 3/4, half and 1/4 swings and use the PW for you normal approach shots at whatever your full or 3/4 approach swing is.

If you are always close enough to the green to need a finesse shot and you aren't using the PW then keep the PW for practice and free up another club. If you have a gap that a hybrid will fill then fill it. Play what you need and use.

I played with a caivity back sand wedge between beginning of 2009 thru mid 2011 (had a set of do it yourself irons) and it actually was pretty good for getting out of bunkers vs even some name brand specialty wedges.   I also noticed it got 5 more yards on a full swing vs a couple blade wedges with the same loft (55*)>

I have been playing with a Vokey 54-11 since I switched my iron set in 2011.  It gets 5 yards less vs the cavity back SW.

As far as the gap between the AP1 PW and the Vokey 50-08 (bent to 49), I have 10* spacing on pitch shots (80 and 70).  It is 15 on full swing shots (110 and 95).  I've been using a 50-08 since last October mainly because my Eye 2 PW was not good around greens or off tight lies (was great in soft bunkers).