Personally I would choose the the XD(M) 40 for the added capacity over the 45. If you are going to reload you can create some very nice low recoil major ower factor rounds for the 40 which virtually eliminates the snappy recoil of the 40S&W round. It's a little more difficult to get an to do this with the 45ACP. I really don't like the snappy recoil of the 40 but some how the XD(M) has managed to tame it a little nd with reloads it is very enjoyable to shoot. There is no doubt that the XD(M) is a great competition gun and with a little trigger work because outstanding.
Sig P220, Taurus PT1911, Browning HiPower 9mm, CZ75, CZ75 P01, Walther PPS 9mm, Savage 9317 BTVS .17, Browning Buckmark, Taurus Gaucho 357 (pair), Taurus Gaucho 45LC (pair), Uberti 1873 Saddle Rifle 357, Uberti 1873 45 LC Carbine, TTN 12 Gauge Double, Ruger Bisley Vaquero 357 (pair), Springfield XD9SC, XD45 Service, XD45 Compact Tactical, XD(M) 40S&W BiTone, Taurus 617 357, Mossberg 500 Tactical