Adam,
both the above are outstanding Hogs, well done.
The first, in particular is a ripper mountain boar with an excellent cape and Trophy.
In response to the opening question, I think that the answer mainly depends on the type of terrain you are hunting most often.
Swamps, open-plains, thickly-forrested mountains, thick crop feilds etc.
Most of my own wild Boar hunting takes place in very dry and hot conditions of Australia's Northern Territory.
Quietly poking around permanent waterholes as well as walking into know bait sites.
Often shooting can be between 50 and 200 yards.
A lot of the times the target Boar is unaware and may be up to or exceed the 100kg body-weight, similar in build to both animals in Ozhunters post above depict.
You want a good amount of impact energy for perhaps 100kg's animal as well as a well constructed projectile that may have to punch through dried mud and 2" thick fighiting pads BEFORE it reaches the shoulder bone.
Most of our Trophy boars are taken by hunters who are there to hunt buffalo and therefore they also take their boar with the same rifle.
And that's not a bad thing.
I'm an in no way suggesting that this is neccesary, but the .375 being the most common, ofcourse we have taken wild Boar with most big bore cartridges.
There are many good Boar cartridges out there, the best choice would be to suit a platform of firearm (bolt, lever, pump etc) to the conditions (terrain), and then choose the best chambering in that platform.
My personal preferences are for a light-weight bolt-gun with a compact scope, chambered in .270, 30/06 or .300 Win mag.
Well constructed projectiles give enough energy and penetration to bring the biggest Boars down at any sensible range in most conditions.
Sorry for the long winded reply..... I love hunting a good Boar !