Hmmm. Now I don't know what I play....D maj is D/F#; the 7th I use in Dmaj is F#/B. In Gmaj, I use G/b and C/Fnat or F#/B. Are those true 7th's or flatted 7th's? No fiddler can bow all 4 strings at once--if the bridge is shaped right and you're good, it is possible to get 3 at once; or you can rock the bow to get a full chord and it sounds like you played all of them at once but you didn't. It's called (I think) a "rolled" chord.

When "chopping" I just don't think it is possible to get more than 2 notes at once. Chopping is that thing that Allison Krause does while she is singing--fingering and sort of beating at the strings way low on the bow.