Being that my pistol is a XD Sub Compact, with a 3" barrel, am I losing velocity with 180 grain that I could make up with a lighter bullet weight ?
Running a heavy bullet gives you less velocity across the board -- so loosing some velocity due to shorter barrel might be a smaller percentage
over loosing more velocity with a lighter bullet.
I think you'd need to specifically chrono the loads you wish to compare from your own pistol. But even after you've done that and gotten raw numbers, what conclusions could you draw?
I think your best bet is to shoot what you might be considering and find which you like to shoot and not worry a heap about the rest. Or look at some real-world chrono results with popular ammo such as those done at BBTI.
Good guys, very interesting testing and results.