Buckshot, my favorite subject. I started hunting when I was ten years old in New Jersey, back when it was a buckshot only state. I have been involved in the taking of many deer with both buckshot and slugs. Some people say that I'm very opinionated on the subject, I would like to think that I'm just passionate. I also have no patience with hunters who don't put safety first. My best friend was shot and almost killed in a hunting "accident", I don't believe in the word accident when safety precautions aren't adhered to.
You stated that you want a 50% chance of killing the deer when you shoot, I believe that you owe it to that animal to be as humane as posible. You will always hear arguements that certain loads have advantages over others, but you can't prepare for every situation so you have to play the odds. If your state allows hunting with a rifle, use one and never worry about using a shotgun. Especially since my buddy was shot, I don't think that anyone should shoot unless they have a clear shot. Therefore a loads ability to shoot through brush is a non-issue with me.
Tons of deer are killed with buckshot every year. When used properly it works, but there is a very large grey area where performance is marginal. A round ball doesn't kill like a rifle bullet, it just makes a hole. A single hole isn't effective enough to consistently kill deer, therefor you need to hit it with several pellets in order to be lethal enough to humanely kill. A single 00 buckshot pellet at 40 yards has the same energy as a .22 long rifle at the muzzle; a .22lr is illegal to use for deer hunting because it's not considered powerful enough. Forty yards is what I consider to be the absolute maximum distance, providing your gun patterns it well. Yes, deer have been taken at longer ranges, but for every deer taken cleanly at 75 yards many more are wounded and considered a miss, only to die later. Think about it, your not likely to miss a deer at that range with buckshot, you'd have to be off by ten feet to not hit him with any pellets, and if your that bad of a shot you shouldn't be in the woods. Over the years I've tagged probably a dozen deer that were shot by someone else with buckshot.
If you hunt in an area where you must use a shotgun slugs are the way to go. A smoothbore shotgun with adequate sights will kill any deer that you hit with it. I have a scope on my shotgun and I can shoot out to 100 yards effectively with rifled slugs. They'll kill beyond that but it becomes difficult to hit due to bullet drop. If you have a shotgun with a rifled barrel and you take the time to find a sabot slug load that shoots well, shots between 125 and 150 yards are possible with practice.