I have to agree with both the last two posts.
Barrel length means nothing for accuracy, in fact, as long as it is long enough to stabilize the bullet, a shorter barrel is less prone to harmonics and vibrations that a long barrel experiences.
A longer barrel usually means a longer sight radius, while that does not mean more accuracy, it means the shooter can be a little less forgiving with the sight alignment and be more on target.
A longer barrel allows more time for the expansion forces to effect the velocity of the bullet. The faster the bullet, the less drop it will experience, so some might say that effects accuracy (yes all bullets drop at the same rate, the faster bullet just travels further), more by allowing you to be more forgiving with your vertical drop guess work.
The faster bullet WILL translate into more energy when it hits something. As for the claim of only 45ft/ps, I am would love to actually put two guns through a chrono and see. I have done ballistic gel with my compact and full size 40 and there is a huge difference, that said, either one would be devastating using the ammo i carry, I have 100% faith in my compact and I use it for daily carry.
No speaking of the .45 specifically, the size and weight of the round is less prone to minor fluctuations than a 9 or 40 which is more reliant in velocity to ensure expansion and energy transfer.