The Citation CJ4 was nearly a separate type rating with a semi-swept swing, different hydraulic system, heated windshield, and an incredible amount of power. CJ4’s are mainly in corporate fleets rather than owner flown due to their complexity and Collins avionics (vs Garmin).  Vne speed of 305knots and an Mmo of .77 are a large step up from other CJ’s. Down low, the CJ4 can cruise over 450 knots, just shy of the Phenom 300 and slightly slower than similar Lear’s.  The cabin is stretched 2 feet over the CJ3 with the same configuration offering even more leg room.  Add in cabin refinements and an externally serviced lav, single point refueling, and it’s easy to see why corporate flight departments love this rocketship.  February 2021 introduced the CJ4 Gen 2 with a refined passenger experience.  Info from the Textron Aviation side CJ4