I have a m&p 9 FS and am very happy with it. When I got it I wasnt thinking so much about gaming with the gun..it was for IDPA, then uspsa, now I am more into the game and sometimes think about buying a 5". I would like to try one before buying one.
I put the apex dcaek and 2 weeks ago replaced the front sight with 10-8 FO.
for range, home, the m&p 9 FS is a nice choice.. the 5" is more for competition, and you can use the FS for competition and be very proficient with it...
as far as accuracy, well, I think the 5" will help beyond 25 yards..and accuracy is more about sight and trigger control, then long sight radius. and uspsa sometimes they shoot at 30" and not sure if at 40" too. and maybe help a little with the recoil for speed shooting