Place the peppers, vinegar, mustard, horseradish, honey, molasses, Worcestershire, salt and pepper in a food processor or blender and blend until smooth, watching for steak sauce consistency. Can be made 1 day in advance and refrigerated.
For the Spanish spice rub:
Whisk together the paprika, ancho chili powder, mustard, fennel, salt and pepper in a small bowl until combined.
Twenty minutes before grilling, remove the steaks from the refrigerator and let sit, covered at room temperature.
Preheat grill to high.
Brush the steaks on both sides with oil and season liberally with salt and black pepper. Rub 1 side of each steak with 1 tablespoon of the rub. Place the steaks on the grill, rub-side down and let cook until golden brown and slightly charred, 3 to 4 minutes. Turn the steak over and continue grilling 4 to 5 minutes for medium-rare doneness (internal temperature 135 degrees F), medium doneness (140 degrees F), medium-well doneness (150 degrees F). Remove the steaks to a cutting board or platter, tent loosely with foil and let rest 5 minutes before slicing. Serve with the Sherry Vinegar Steak Sauce on the side.