Probably won't be able to keep them both comfortably in either. I would recommend one with a 24 inch width and 6 foot length (pretty sur a standard 180).
Everytime I read about disasters with RD in cichlid communities (aka more than just the red devil in the tank) it ends in death.
But there is a guy on here who has 7 red devils in a 150 and they are doing very well, but you wou dlneed to get more than just 2 to let the overstocking thing work.
Its tricky, but I think if you overstocked a standard 125 would suffice.
Good luck, have extra tanks set up and dividers and view blockers in the tank prepared.