The wildcat cartridge 6x52 Bretschneider is just the 5,6x52 (.22 Savage Hi-Power), necked up to 6 mm. I think the 6x70R edges it out a bit, probably because of slightly higher breech pressures and perhaps, being a newer era carridge, it may have stronger brass. It might also be a bit more of a challenge to find published reloading data for the Bretschneider, especially in English.

Given that the hog deer is in much the same class as the roe, (perhaps a bit bigger), the 6x70R, 6x52R, 5,6x52 and 5,6x50R should all be in the same ballpark. If you're not restricted to a break-open gun, the rimless version of the 5,6x50 (a Heym development), is going to have the best trajectory & retained energy compared to these rimmed cartridges.