Have Ruger .454 SRH with 9 1/2" bbl. Have worked-up some pretty good loads with various 300gr. cast bullets using H110. Would like to extend my accuracy [inside 100 yds.] and hunt whitetails and hogs.

Question: Need recommendation of brand/power/reticle for the SRH? Fixed or variable?

I have excellent experience with Nikon optics on my rifles. But I am completely in the dark as to handgun optics.

Any advice from experienced shooters/hunters on my scope inquiry will be greatly appreciated.

Most handgun scopes don't gather enough light for me, for those early or late shots. The long eye relief does something that makes light transmission poor. Many times I could not see either the crosshairs or deer through them. By the time it gets light enough, most of the deer are gone.
Recoil has also broken many scopes for me. (And some cheap red dots.)
I only use the Ultra Dot, red dots now. The Ultra Dot will take any recoil without shifting POI or breaking.

I started out with a Leupold fixed 2x and then upgraded to a Vari-X III 2.5-8x32 on my .454 Casull. Both scopes provide excellent light transmission for shooting at dawn or dusk. I like my ordinance on the hot and heavy side and have never had an issue with breakage or shifting POI with either scope.

I have a both a Leupold 2x and 4x mounted on S&W 500's and neither one of them have failed yet. I've also got a Burris variable mounted on a .460 S&W that's held up. If I were going to limit the distance to less than 100yds for deer I'd go with the Leupold 4x

I have a Leupold 4X that has been on so many big bores I can't count them and is still perfect. Great scope but it is still too dark in the AM. I have a Tasco 2X that holds up to the .475 but I can't see a thing through it in the AM. I have a Burris that is like looking through a black hole any time of day.
It is a problem I don't have with even the cheapest rifle scopes.
If all of your shooting is when it is bright outside, fine, but the best time is still early and late in the day. I hate waiting an hour after legal shooting time to be able to see anything. Too many times I have had to pass on deer because of dark scopes.
I will never hunt with a regular scope again!