I mean... I guess that's good advice, but I don't know what I would convert to SMD, considering that all but a small handful of my components are already SMD. I really don't have signals on wires (the down-converted AF signal passes between boards, of necessity, and I was able to rule out that as a factor in the internal noise floor). I have full ground planes, but these are 2-layer boards so it's not so easy to run power planes. I'm pretty sure my A/B test with the two regulators is a very strong indicator that the R-78E regulator is (A) a challenge to work with in the best case, or (B) just not suitable for this use in the worst case.