M8 4x33, if I understand this correctly, does not have Multicoat 4. It is single layer MgF coated. The only M8 scope with multicoat 4 was a 6x42 (a decent scope, but not top in its price range either). The new FX-II 4x33 does have a Multicoat (and is an excellent scope, byt the way).
On top of that I think that a M8 4x33 has friction adjustments instead of click adjustments. I do not know how much difference it makes though. That's certainly a personal choice as I like click adjustments.
As for Leupold's warranty, while it is a nice feature, I've never bought a scope because of the warranty.
Basically, what I am trying to arrive to is that I think Weaver K4 is a better scope (IMO) than Leupold M8 4x33, and yes, I have seen both side by side. At lower magnifications the difference between different glass is not as pronounced, but it is still there especially in low light. I was once curious about this and I took a few 4x scopes I had at the time out to compare them after sunset. Not surprisingly IOR was the best one (and the most expensive one) I have. Burris 4x20 suffered a little from a smaller exit pupil. Sightron S2 4x32 was very good and Weaver K4 was not all that far behind. Leupold M8 4x33 suffered from inferior optics, but had very forgiving eye relief roughly equivalent to SIghtron's eye relief. Although, Burris 4x20 has longer eye relief and would be my choice on a kicker. Interestingly I was not especially impressed with Nikon Buckmaster 4x40, but Monarch 4x40 was very nice, albeit pricy.
Of the expensive German scopes, the onyl 4x I've seen was a Kahles and although I did not spend too much time with it, it did not offer any advantage over a much cheaper IOR 4x32.
Of all the 4x scopes I've had over the last few years, I've kept two: Burris Compact 4x20 and IOR 4x24 tactical with CQB reticle. Unfortunately, I traded my Sightron, but I might get another one.