The Sightrons have a big following in the BR crowd and Nikon is always a good piece of glass. Between the two I would go for what gave me more of what I wanted personally. If you are looking at shooting small groups on paper I would go for the most magnification as I can see you are doing. I know many use low power 4x to mid 6-9 for most target work but for me I like the most magnified view I can get for shooting even 100 yards. The bigger the POA looks the better for me as the more I can see the movement I cause and the better I can work on it. The ideal magnification @ 100 for best line up for me is when the 1" box grid line lines are at least the same size as the cross hair lines in my sight picture. Not saying its right but it is what allows me to shoot my best groups.
One thing you need to realize with these scopes is exit pupil size. The smaller it is the more y9our weld will be critical and the harder to find it will be. The bigger the obj lens the better the exit pupil given the same magnification so I would be looking at that. 50 would be good. but even 42 works. Many use even the 36x with them and that is a very small exit pupil indeed.