Hi Beowolf,
I’m no expert and can only speak from experience. The trips I have done are mainly driven and I used a .270 on the first trip with 150 grain Nosler Partition ammo and they worked fine, but I always felt under gunned, when I looked around the guys on that trip, the range of calibres’ was very varied from my calibre up to the 9.3mm over and unders with open sights.
After that I used a 30.06 with 180 grain Nosler Partition ammo, again this combo did the job just fine, 30.06 and 308 seemed to be very popular with guys who do quite a lot of Wild Boar shooting be it driven or high seats, But like most things it is personal preference, but if were to pin me down 30.06 or 308 are fine and for longish shoots from a high seat they may have the edge from some of the bigger calibres but watch this someone will not agree its just my opinion.
Good look
Smithy