For what its worth, here is my experiance:
Like everything else, it depends on the round. Wadcutters make a good hole and cause damage, but you need to keep the velocity up. Alot of the WC rounds are meant for target shooting. Buffalo bore and some other folks make defensive load wadcutters if you look hard enough, and also 'hard cast' which wont deform which helps on the gel tests I have seen. Based on my research, all else being equal, the 'right' wadcutter outperforms a FMJ.
With "high-powered" rounds, I have seen ballistics tests where .32 caliber wad-cutters perform amazingly well, almost on par with 380 or even standard 9mm, in terms of penetration depth and wound channel diameters. So I believe whatever caliber, if loaded right it is a round that can punch up out of its weight class.
I mention this little guy (.32) because I studied it alot more than others with regards to wad-cutters. It has always been considered the most inherently accurate round, and with so little recoil even a novice can be good with it. Whatever your carrying, it only helps if you can put the rounds on target. We really became a "bigger is better" gun group as americans, and everyone wants something with a larger caliber that makes a bigger hole. Thats fine for most guys, and if you just carry a tomahawk missile you'll never be outgunned. I was curious about how much is too little and what was overkill so I could figure out how small and manageable a gun could be and still be guaranteed lethal, so I spent a lot of time studying this to try and properly arm my wife with something she would actually carry, and be able to use well. I started at .45 and worked my way down and when she got to the .32 she could put 5 of 5 in the center with rapid fire from 7yds, and thats what I wanted. But the .32 rounds are generally weak, so I looked into how to make them more consistently lethal without loosing the 'shootability'.
On low velocity rounds, like the 32, you often will not have the velocity for a hollow point to work. So besides everyone not liking the small diameter of the round, and then the mostly anemic loads that are easily available, you then apply what works well for a 38spl and it performs like **** on a 32. I know hollow points are not an issue with 9mm and 38spl, because they dont have a velocity issue. However, a wadcutter is already full diameter, almost like shooting already 'expanded'. Plus it 'cuts' the tissue, where the rounded-nose jacketed slugs 'push' tissue out of the way, so the wound channel closes back behind the bullet. A bigger hole is better, because it means more tissue and blood loss. The gel tests I have seen show a wadcutter cutting a much larger hole when compared to a same size FMJ, so a larger wound path with the WC round (all things being equal). I think we all would agree a bigger hole is better. Of course if you carry a 45 or a 500 your making a bigger hole, but I am not a big guy and found myself leaving the 45 in the car too often, and again, doesnt matter if its a bazooka if you dont have it on you, so I moved down to a 38spl because it never leaves my side.
There are drawbacks with power with the wad-cutters, and with rounds under 9mm. but velocity is velocity and as long as you have enough the wadcutter will penetrate leather jacket, sweater, shirt, skin, bone and tissue. I see 15" penetration with good .32 in the gel, and thats through 3 layers of clothes. Once your over say 900fps (which is like 615mph) the bullet is going to penetrate, and I wouldnt want to be shot with one to test it in person.
So, yes, carry the largest caliber that you will carry consistently, but past that I think a good wadcutter load will do more damage than FMJ, but maybe not as much as a hollow point with larger rounds like 38spl or even 9mm. Where velocity becomes a problem (like 380 or .32) wadcutters seem to make up some of that difference and perform well, when loaded right.
Thats one persons research, take it only for what its worth... I'd always recommend buying some ammo and performing your own tests.
