Make cuts 1/2 inch apart and 1/8 inch deep in a cross pattern for both sides of the beef.
Put beef in a sealable zip lock bag.
Combine red wine vinegar, brown sugar, beef broth, soy sauce, honey, ginger root, onion, garlic cloves, and red pepper in small bowl and mix.
Pour this mix over the beef and seal bag. Refrigerate for 4-24 hours.
When ready to grill, heat grill.
Remove beef from marinade and set marinade aside.
Grill beef 4-5" from medium heat for 12-14 minutes for medium meat, brushing twice with marinade and turning once.
Add nectarines to grill for last 5 minutes of grill time.
Discard leftover marinade. Cut beef across grain, and add sliced nectarines.