I've done quite a bit with both the XTP and Gold Dot in 9MM, .357 and .45. Both are fine bullet choices. In some cases I've found the Gold Dot to have a slight edge, in that the XTP's will separate while the Gold Dots won't. With the .45 Colt specifically, the 250 grain XTP works fine from 950 up to 1450 FPS MV, the range I've tried. The 230 grain Gold Dot shouldn't be driven much faster than 1050 FPS, its construction is too light for higher velocities. (I didn't believe Speer, tried it. They weren't lyin'). With any high velocity .45 Colt load, XTPs would be my choice. With anything else, I prefer Gold Dots. Both expand properly, but that weight retention/separation thing gives GD the edge in my opinion. Right now, I have several hundred rounds of .45 Colt loaded with that 250 XTP, at a MV of 1400 FPS from my Blackhawks.
DC