Yeah, this movie is great. I'm lucky that I got away mostly unspoiled.
So, Mjolnir and pre awakening thor would probably be High 6-B now. Which kinda makes sense if you think about it. Thor awakening was just realizing he didn't need his hammer. We only assumed it increased his power because it didn't show any other feats on that scale. Now that we have said feats, we should be able to upgrade safely. That said, Cap did hold Mjolnir for awhile and used it in a major fight, even showing he's able to call it to him like Thor, so, he should be able to get it as Optional Equipment, and thereby a High 6-B key. Oh yeah, the shield should also be High 6-B for tanking Thor's hammer, along with several blows from an aggressive assault on Thanos' part.
I want to get a calc on avengers base blowing up. Literally everyone tanks it, including Ant Man and all the 9-As, so it should scale. Dunno if we'd have to account for surface area or the fact that it took many rounds to make such an explosion, but either way it would definitely look cool. Also, Giant Man does frag some rocks as he tries to get hulk and bros out of the rubble.
Thor was able to draw Stormbreaker all the way from New Asgard to Avengers Base within a few seconds, so that's probably an MHS+ supporting feat if we looked into it.
Spider Man's instant kill mode is probably some form of instinctive reactions, as it started attacking the CGI mooks all around him automatically, only stopping when they manually grabbed it to dogpile Peter.
Generally this movie is awesome and the feats are awesome too