Another good tip that I picked up here is to use a drop of dishwasher soap with water in the pitcher to simulate milk. It actually works really well and is a great way to troubleshoot without blasting through gallons of milk.

For latte art, buy a bulk can of soy sauce for the espresso and use the soap water for the foam.

One thing I learned the hard way was to thoroughly wash out the pitcher after each use. And when I say use I mean each session - not necessarily after each drink. For some reason that made a huge difference for me, apparently rinsing it out with lots of hot water was not good enough.

GeneG wrote: I've got microfoam rising up and spilling out and over and everywhere, all paint-like and rich. One glorious mess!
12 oz pitcher will be my next purchase.

IIR youir technique C, you're using five ounces of milk (ish) in a 20 oz pitcher, and you're getting foam coming over the top? That sounds a bit wrong...
OTOH, if you are really getting that much foam, why're you considering going to a smaller pitcher?
If I've misunderstood, please feel free to ignore all of this...

As a general rule it's good to have the pitcher about 40% to 50 % full (give or take.) With I do 4 to 6 oz milk regularly and always use a 12 oz pitcher. My 20 oz pitcher is reserved for the occasions when I have guests and steam for two or three drinks at a time - then using 10 to 12 oz of milk.

You should not be expanding the volume of the milk by any more than 15% to 20% so that smaller pitcher will be just fine.

As for milk... I've run into the same issue and it always seems to be when the feed mix for the cows goes through a seasonal change. Might be coincidence but I doubt it. 90% of my milk use if for my own cappas and machiattos so I bite the bullet and buy organic milk. Last time I had this issue I switched to locally sourced non-organic, the problem went away and then I went back to my previous ilk a week or two later and all was well again.