It's been a while since the Pure Control Swirly +, but I still remember the rock-solid shots I got from that thing. In particular, my running cross-court forehand. That was thing of beauty w/ the Swirly. If you look up 'plow through' in the dictionary, you'd see this photo:
but I digress...
The X Force Pro does not have the punch of the Swirly. It is truly a control-oriented frame. However, one of the complaints from old Pro No. 1 users is possibly one of the things I like most about it: It's "stiffness".
Obviously, it's all relative, and I can tell a difference between the M Pro No. 1 and the X Force Pro, but again, for me it is a positive. The frame still has the Fischer feel, it's just a bit muted than it's predecessor. The power is there if you swing through it, but it is real, real stable.
Not to get too technical, but while I'm mostly a singles player, one thing I rely on in doubles is return of serve. My volleys are decent, as is my serve, but I'm not going to blow you away with either. However, my service return, in particular, the 2HBH, is where I do my damage. The first thing I noticed when demoing this was how accurate I was with my return. Some of the guys I play against bomb the serve in at 120+, and right away I was able to drive it back at them, up the middle, cross-court, flat or with spin (I usually return from the ad side). High kick serves? No problem handling the shots above the shoulders. Just drive through & the shot is at their feet.
All in all, a great frame for 4.0+ players.
BTW, I string mine w/ Pacific Classic 17g mains @ 58, MSV Co Focus 1.23 crosses @ 56.