No change.
If a HP clogs, then it doesn't expand and degrades to FMJ. In such cases, larger is definitely better IMHO. I think it is important to distinguish between soft tissue penetration and hard object penetration. I'm going to simply this, but...
For example, cartridges that are designed to penetration armor focus on small area and velocity. They defeat the armor by focusing the energy on a small area which causes the armor's bonds to essentially "break" at that localized area. Propel the projectile fast enough and you don't even need that hard of a projectile (or that heavy) to defeat serious armor. If you have ever seen a rail gun test, you know exactly what I mean. Energy is mass * velocity^2 (or mass * velocity * velocity). Clearly you gain more through high velocity than more mass.
Armor defeats projectiles in two ways. First, it generally works by absorbing and spreading the projectiles energy over a larger area. When ceramic armor fractures this is exactly what it is doing. Second, armor is usually designed to be very hard (AR500 steel, ceramics, etc.) so that it can shatter the projectiles penetrator. The idea is that you turn the energy in the penetrator against its self. Shattering a penetrator uses up a lot of energy. Also, it goes without saying that the remaining energy is no longer focused on a small area.
Try this thought out. Most LE wear Level II-A vests which are capable of stopping virtually any handgun threat (IIRC the new NIST standard uses the 125gr .357SIG for penetration tests and 180gr 40SW for blunt trauma). The Kevlar (or similar) works by spreading the load out. Bigger/heavier rounds posse very little penetration threat, but they are potentially a serious problem for blunt trauma as the body still absorbs a lot. Level II-A will stop 9mm out of a handgun, but not out of a SMG (technically it might, but it isn't tested for such until III-A). Same round, same weight, but just more velocity. Rifles go through soft armor like butter. Again, the idea is that you defeat the armor by dumping a lot of energy in a small area and simply overwhelm the local bonds.
Explosively Form Projectiles, do the same thing. The explosive doesn't defeat the armor, it is the liquid material (usually copper) moving at high velocities that is focused on an area about the size of a pencil which defeats the armor. Cages and reactive armor defeat this threat because they disrupt that stream. The EFP stream has very high energy, but very little momentum by comparison. If you spread it out even a little bit it doesn't do jack diddle.
On the other hand, momentum is much more useful for deep penetration of softer materials. This is why we have the general rule of thumb that "heavier" rounds penetrate more. Momentum is mass * velocity. No advantage to upping velocity vs increasing the mass (units matter, but roll with it). Taken from the Wikipedia momentum page:
I.e. the more momentum something has, the more force that must "push" against it to bring that velocity to zero. In layman's terms, the more momentum, the more stuff it can push aside before stopping. It should be apparent that larger calibers have to push aside more "stuff" for the same penetration. Assuming no expansion a rough estimate says that a .45 pushes aside approx. 1.6x as much stuff as a 9mm. In order to penetrate the to the same depth, the .45 needs approx. 1.6x as much momentum.
I'm grossly over simplifying it, but you get the drift. Harder objects like metal and glass favor "velocity penetration" (assuming the projectile stays intact more or less), while softer materials "momentum penetration." The problem with leather and skin is that they are very elastic and spread the loading out. Not to the extent Kevlar does, but skin is worth a good inch or two of gel. I need to look this back up as I don't recall the actual estimates, but this supports the point:
Also, skin is elastic and tough enough to cause a bullet to be retained in the body, even if the bullet had a relatively high velocity when it hit the skin. About 250 ft/s (76 m/s) velocity is required for an expanded hollow point bullet to puncture skin 50% of the time.
Personally, I just use good HPs and don't worry about it. While caliber wars are fun at times, the reality is that with modern HPs the four common calibers (9mm/357SIG/40SW/.45ACP) are very close. Some calibers are slightly better at certain things or more precisely certain tests, but shot placement always matters more.
