The basic rule is that the more a bullet tends to expand consistently to a certain shape, the more it penetrates at higher impact velocities. I've found this to be generally true of Barnes X's, Nosler Partitions and E-tips, Trophy Bondeds, North Forks, etc.
When a bullet tends to expand more widely at higher impact velocities, the less it will penetrate. This category would include Hornady Interbonds, Norma Oryxes, Speer DeepCurls, Remington Core-Lokt Ultras, Swift Sciroccos, Woodleigh Weldcores--and even, to a certain extent, Swift A-Frames, because the rear end also tends to expand at high impact velocities. Also inclused would be cup-and-core bullets.
These "rules" aren't hard and fast, because other factors affect penetration. But in general the area of the frontal mushroom affects penetration more than weight retention, as well as impact velocity.
