This is a topic that has been debated before with no clear right or wrong decision. I go back and fourth with the same decision but with the pitching wedge. Some people will say the gap wedge is typically a "full swing" club and therefore should be part of the iron set. Others will argue that the gap wedge is a "scoring club" and therefore should be a true tour wedge. What everyone agrees on is that from 120 yards in everyone wants to hit the club that will get them as close to the pin as consistently as possible. If you're having difficulty with the ap2 wedge and are more comfortable with a Vokey wedge then put the Vokey in your bag and start shooting lower scores. Your question/observation that the AP2 gap wedge is flying further than you expect is an interesting observation. Many people believe that you will lose a little distance when using a tour wedge as opposed to a wedge designed as part of the iron set. I personally don't think that one is longer than the other. Two clubs that have the same characteristics (loft, length, swing weight, etc.) shouldn't be measurably different in regards to the distance the ball travels. My belief is that the wedges that are part of the iron set are more forgiving due to cavity back and perimeter weight designs relative to tour wedges so we perceive the wedges that are part of our iron sets as being longer. 

Just put in a 46 degree sm5, just one degree stronger than an AP2 pw.  Love it.  

I went with the Vokey gap wedge.  For me, I was looking more for control, spin, and versatility than I was distance.  I felt the Vokey wedge gave me that.  I really don't hit a lot of 100% power gap wedge shots (which is where I feel the AP2 GW would help), but I do use my GW for a lot of chips and pitches (which is where I feel the Vokey GW excels).  It comes down to personal preference and what feels the best, but in my opinion, you can't beat the Vokey wedges.