Last year I did an open jaw trip to Chicago Amtrak-ed it to Memphis and then rented a car to Nashville. I flew back on CW with BA from Nashville.
I'll be honest the flight wasn't great from Nashville - there was no lounge at all just a 30USD meal credit. The plane was also old CW with the ying yang seats and the meal was not great either (see pic).
I'm not sure what aircraft BA are flying on this route now but with the club suite and 'Grand Lobby' lounge open I think this would massively improve it.
I've got to say that Memphis was great and if you're into music and planning to do Graceland, Sun Studios etc. it's well worth it.