I wasn't feeling too great the last few days so I wound up freezing the marinating butterflied sirloin for fajita that I had left - but I left one in the fridge and it continued to marinate (extra virgin olive oil, smoked paprika, hot red chile powder, cumin, Mexican oregano, crushed fresh garlic, fresh squeezed lime juice, Kosher salt, AND, a diced ghost pepper (seeds removed)).
I just cooked it for breakfast with an egg and that steak was so tender that I cannot even describe it - it was fricken awesome. I think the lime juice in the marinade may be what did the trick!