Good starch to go with Grilled whole Filet
I love sweet potatoes with beef. You could pre-steam wedges and finish them on the grill and serve with a sriracha or herbed aioli which is good on the potatoes and the beef. An herbed farro or orzo salad would also be good and could be made ahead of time.
I enjoy steak with new (yukon gold) potatoes slathered in olive oil and sea salt. When they're done, I like my potatoes fork tender with a golden brown crust on the skins. Serve with greek yogurt and chives...yum!