I like my G20, but I LOVE my G40 in 10mm. If you want a semi auto, I'd go 10mm all day long. I've killed pigs with a 45 and 10mm, and the 10mm is hands down better with more energy and much more penetration.
I agree with the above about the 10mm being a superior caliber for this duty. I also believe bullet selection to be way more important than caliber selection. I cast all my own slugs and size to fit each gun they are fired from.
What ever you choose, a hard bullet with a big meplat is best for penetration as well as tissue disruption. These can be tricky to get to feed from semi auto platforms at times.
Hogs don't take anymore killin that a whitetail. Its all about shot placement.
Find something that you are comfortable with and can shoot very well.
I have a 38 special load with Keith style slug that will flat bore a hole straight through a hog at short range.
If semi auto were a must, I'd choose the 460 Rowland as I alreay have all the set up for .452 bullets. They make a conversion for 1911's as well as the Tupper ware plastic guns.