I've been using the X Force Pro for a little over a year now, and have no plans on changing in the future. For my game (4.5 version of Ferrer), it is the best frame out there. Tons of control, great balance & plow through (especially on service returns), not very powerful, but I can swing through the ball with confidence.
I used the M Pro No. 1 for ~ 2 months before deciding to get X Force Pro, which is effectively the 'Black Granite' M Pro No. 1, a slightly stiffer version of the M Pro No. 1.
I assume the X Force is essentially the X Force Pro, but with some weight removed from the handle as the balance is only 3pts HL for the X Force and 8pts HL for the Pro.
57lbs is probably spot-on for full multi, however I've settled on 17g gut mains (Klip or Pacific) @ 54lbs, MSV Co Focus 17 @ 52lbs, a great compliment of feel, power & spin.
"Nobody beats Vitas Gerulaitis 17 times in a row" -- Vitas Gerulaitis, after beating Jimmy Connors on his 17th try.