Unfortunately, in describing the situations in which you'll be taping, some of those I would say the MK4 is the better choice and in others the MK41. You've described a scenario in which you need a one-size-fits all-capsule that doesn't exist...at least not when you've put forth the question in the context of 'should I get MK4 or MK41'. For your taping needs, I think the best answer is to get both, but that's not what you asked.
That said, for stealthing, unless you stack tape and the volume of the music drowns out the chatter of the audience, I don't think you can eliminate chatter with capsule selection, no matter whether you're using a 4 or a 41. After all, what's the difference if you hear the chatter from the people in front of you or a few more people that are in front and beside you. Chatter is chatter on a recording, no matter where it's coming from. And lets face it...yes the 41 is nice and directional, but it still will pick up the chatter of the people that are standing to the side of you (although maybe the level of the chatter coming from the sides will be attenuated slightly). Look at the polar plots, the 41's side rejection isn't absolute, so side chatter is still going to be heard when you're standing amoungst the talkers (not to mention that a 41 has a rear lobe that a 4 doesn't have, so rear facing chatter is an issue for the 41 if you're standing in the crowd). That said, there can be a huge difference when the capsule is suspended up above the crowd, yes for sure the MK41 is effective at minimizing the chatter of the people that are 4 to 6 feet beneath the capsule location. But standing in the amonst the chatter...not as much.
So, I think the answer then falls back on Page's comment about reverb, room dynamics, and even more important WHERE YOU RECORD FROM in the room...but with the added point that your best capsule choice is dependent on where you do MOST of your taping. Your answer really becomes quite simple then...at least to me. If you record mainly in closed in rooms and especially rooms that sound reverb-y or where you have to stand back enough that the sound breaks up, then I think the best capsule for you is the mk41 since that's going to give you the most bang-for-buck for your single capsule choice. If you record mostly in open spaces or rooms that sound really good wherever you are able to record from, or you're always able to stand in the best sounding location in the room, then go with MK4 for the same reason.
EDIT TO ADD: About your windscreen question...it makes no difference, both 4's or 41's will require a screen when you're outdoors although I suppose your hat or whatever could be an effective screen depending on the material.