I have been shooting a Beowulf since the around 2002, before that, I had a Tromix 50AE upper. My Current wulf is from A.A. with a few personal tweaks to it.....But there is something impressive about shooting sub MOA groups using 1/2" projectiles. Since people usually invest a fair amount of money into there choice of caliber, between the upper/rifle, ammunition, reloading components, they do not want to here that maybe they did not choose the best and will strongly argue for there choice. So take what you hear with a grain of salt.
In all honesty, both are good choices, and you will be happy with either. are there more projectiles options for the 458, yeah probably....but are you going to be loading ALL of them, no....in all honesty, you will probably only load a handful of different weights on a regular basis. I pretty much stick to the 325 to 350 weight range with My beowulf. I know how they shoot, where they shoot, and what the do when they hit. Do I have lighter and heavier projectiles, yes, have I loaded them yes, in smaller amounts for the fun of it. Looking the real extremes on the weights, have to consider how well they stabilize with the twist rates on these barrels....a 100 grain 458. what is the point, I'll grab a 6.5G or 6.8SPCII at that point....
I like the Beowulf. I would not mind a 458 also, but really do not want to get setup with new dies, brass and projectiles to reload another caliber....that has been the biggest reason I have not also gotten a 458 up to this point.