Citation III (Model 650) all-new design.[16][17][18] Citation IV was a proposed upgrade of the III, but was cancelled by Cessna.[16] Citation VI (Model 650) was a low-cost derivative of the III which had a different avionics suite and non-custom interior design.[16][17] Citation VII (Model 650) was an upgrade of the III that was in production from 1992 to 2000.[16][19] Citation X (Model 750) (X as in the Roman numeral for ten), an all-new design, the fastest civilian aircraft in the world since the retirement of Concorde.[20] 24 feet (7.3 m) of stand-up cabin space.[21] Citation X+, originally called the Ten