No difference in light, stronger tube, and the 30mm will allow for a wider range of zoom, lastly to allow the use of better optics. Not all companies utilize the extra space for upgrading optics, as mentioned above Leopold is one of them.
If you want a nice scope with significantly better specs than the one you are looking at you may want to have a look at the Bushnell 6500 2.5x16 42mm, it is much cleaner to look through than the VariIII, also it is 30mm, side focus and has a continuous eye relief, which the Leopolddefinitely doesn't.
Big decision to make, do yourself a favor and find a shop that will let you look through them outside, technology has taken huge steps in the past couple years, Leopold is no longer making the scope they once did.
Another bonus with the 6500 is the rainguard, this thing can go from cold to wet to warm, breath on it and you can still see your game, no other scope does that.
In the price range you are in you may want to look at a Zeiss too, another decent scope, minimum features though.
Good luck, pick something your eyes love!