Google-fastest Supercharger-Supercharger:
- Springfield, MO to Atlanta, GA or Nashville, TN takes US-60 through Miner, MO.
- Little Rock, AR to St Louis, MO takes US-167 and US-67.
- Springfield, MO to Memphis, TN takes US-63.
- Springfield, MO to Little Rock, AR takes US-65.
Hmm. A whole lot of hole you got there.
So, in addition to completion of I-40, I'd be arguing fo(u)r:
- Willow Springs, MO
- Poplar Bluff, MO
- Walnut Ridge, AR
- Harrison, AR
Then the quadrilateral of Springfield, MO, St Louis, MO, Little Rock, AR and Memphis, TN would be covered.