So here I am, looking through some older speedpaints, and I realize how much I enjoy the look of the looser strokes I was using when I didn't really care about the outcome, and I knew nobody would be seeing the end product (unless I wanted them to). Part of the reason for this look is that I was teaching myself how to paint in Photoshop and wasn't bothering to noodle in the details - just focusing on the broad strokes and learning how the brushes behave. I don't necessarily dislike the tighter rendering I've used on the Captain America covers, but I really want to use a more painterly style eventually. We'll see if it happens.
For the record, this was done from reference sometime last year.