Fin based failures are generally based on 3 things: Fin Shape, Fin Material, and Fin reinforcement.
A clipped delta with a short span is generally the best when it comes to keeping the fins on. So "smaller fins" wont mean more probability of a shred, it'll generally mean the opposite.
A stiff fin material will also help with flutter and vibrations. Stiffer fins mean that less force is put on your fin attachments during flight. You used 1/16in G10, which is acceptable for a 38md. I've personally flown 1/16 G10 to ~Mach 1.8-2.0 in a 38md. However, that was a fin shape designed with a high stress flight in mind.
Of course fin reinforcement is also important. Those tiny Jb weld fillets won't do much. The bigger the fillets, the better (within reason). I don't think you'll need any "tip to tip" in the 38mm size so fillet strength is very important.
Looking forward to the rebuild!
Alex