Well, this still sounds like a 9mm/.45 debate. Buy the gun, Glock or Ruger, that you feel the most comfortable with, then buy it in the caliber that you want! If you like the Glock, get a .45 Glock. Don't pick the P90 just because it is .45, there are LOT's of guns available in .45. Buy the one you want. Personally, I prefer my Colt Defender .45 to either. 44 Man