Dirtfarmer, it sounds like you have plenty of experience, so whatever you come up with should be good enough for your buddy. Those Nosler Partitions should do great.
I've played around with a bunch of bullets and powders out of my .416 Rem, both solids and softs. I ended up using the 400 gr. A-Frames for softs. My backup was the 350gr. TSX and I'm sure that would have worked just fine, but I prefer the bonded lead bullets and the A-Frames have an excellent reputation in Africa. I did mess around some with the 400 gr. TSX, but that bullet was a tad too long and the velocity, of course, was reduced. For solids, I preferred the old North Fork solid. Not sure if they are available now or not, but I'm sure the Swift solid you just purchased should do the trick.
As for powders, RL-15 was the best for both the 416 and 375, in my experience. I did use IMR-4064 some and that did OK as well.
By the way, my PH in Zim had the same philosophy, i.e. load a soft up the pipe and fill the mag with solids. Not really what I would have done, but he was the boss so I listened.
