Well, malus 7 will be a lot quicker, especially because malus also rises less quick. Alts can be used at that setting quite for a long time though, thats right.
Malus 4 is a very special setting, taking a lot of time, knowledge and effort. New eco was built for that setting, you can feel it. I'd still prefer malus 4, because malus is punishing you hard raising 20% per level (as far as i know, maybe 15%^^), no quickies. Double the POIs is actually a smart idea I think, making "luck" a bit less of a factor.
Something "new" like malus 5 with the punishing rising setting from malus 4 would probably be interesting, enabling to switch to the next tunnel more quickly, reducing the overall time, but still needing a lot of insight for longterm eco and main. But farming would be brutal at malus 5 i guess. :D
m4 or m5, my 2 cents. m7 is a bit too easy without FA for the best battling