I'll do about a quart of buttermilk in recipes around the holidays, but I've been leaning hard on my sour cream mixture.
I increased the amount to 3Tb per cup of water for my lemon pound cake, and I'm thinking about adding more. Testing the possibilities before summer hits and I bake a million loaves for when I go visiting.
I make a German chocolate cake once a year for my partner's birthday that uses an absolutely horrifying amount of sour cream. 12/10 would bake more if it wasn't such a pain in the ass.