I've not tried the Sightrons,nor the IOR Valdala. I have tried the Nikon and Leupold's FX II's and III's. I like the FX III's the best, followed by the FX II's. The Nikons I got through that SWFA fiasco, and they are nice scopes, but I think the Leupolds beat them in eye relief. Aren't their maintubes a bit shorter, too? With the scope mounted as far to the rear as the leupold rings/bases I had on my M700 SA would allow, I had to crawl the stock to get a proper sight picture. The Nikons went down the road.
Currently, though I find myself a bit flush with 6x's, might need to unload one/two (cheaper than buying rifles).
Kaiser Norton.
