I know you said "fixed position", but I had a PRS Magpul put on my AR 10. With it being adjustable, I found it very easy to set up to fit me perfectly. Not only for my LOP but also for my cheek weld height. I also think the slight added weight would benefit you greatly by balancing that .458 out a good bit. The skeleton stocks, to me anyway, just don't feel right. Not to mention that if you load any heavy loadings up in that beast, you will be thankful for the larger size of the buttstock end on the PRS. That skeleton stock would flat out hurt with a heavy load from a .458.