5.8 cents/mile is very expensive. Are there any flights where you can squeeze in more domestic legs? 7840 RT miles sounds like a direct route. Flying in J, you might as well trade in more miles for that expense.

ORD-FRA-LHR-BOS-STL-ORD is 9700 base miles, pricing say $3500 or 3.6 cents/mile on J (or better). I'm sure the mileage wizards here can come up with cheaper routes.