I've never owned the 2.5X scopes mentioned. But I have owned the older M8 or M7 3X, and now have the latest 3X, the Dangerous Game Scope as it's called. The image on the new scope is noticeably sharper. But, that might be because I bought the scope used, and it was used/cleaned a good bit on several rifles and one very light, slug firing shotgun over the years. Image quality will degrade over the years from even the best cleaning methods I'm told. BTW, it never failed to hold zero, even after 250 plus rounds of magnum class rifle slugs fired through a light Ithaca 12 ga. pump.
You might want to try contacting Phil Shoemaker about these scopes. He has used them a lot. E