I have shot both of these bullets, the 460 No Excuses extensively, the Hornady FPB just a couple times. I would go with the KNOWN variable when it comes to elk hunting. Like others already stated, the Hornady FPB is NEW, and UNKNOWN as to terminal performance.
Do I think the Hornady FPB is capable of taking an elk, yes, but I know what a big ole 460 NE will do. Besides, you can crank up the 460 if you want to, you will have to keep your powder charge down a bit on the 350 FPB IMO.
I have shot both of these bullets into my little torture chamber,
I don't have a pic in my files of the 460, but I have a 430 grain White conical that looks similar when expanded. The FPB did well, better than I expected I will post pics of also. This test is just a qualifier for any bullet I will consider hunting with, and lesser bullets have failed.
White 430 grain Super Slug, 80 grains 777 FFFG
Hornady FPB, 80 grains BH209
For comparison, the Hornady/TC 300 grain SST/Shockwave, 80 grains BH209
And a .45 cal Hornady 300 gr XTP/MAG, 80 grains BH209 (these are tough)