I don't think there will be a noticable difference between the two. But I do think there MIGHT be headspace/shoulder issues with the Whelen AI since there isn't much shoulder to start with. If the 350 will clean up the chamber of the 358, I think that would be MY choice simply because brass doesn't have to be formed like on an AI round.
The only complaint I've read about the 350 is having to short seat the heavier bullets in order to fit in short action chambers, but that should be a non issue for a single shot, especially if you throat it to the bullets you want to shoot.