I was talking to someone who just got his multi-rating and was excited that he got to fly a Cessna Conquest. He didn’t think he could log the time because it is a pressurized plane capable of flying over 25,000′ and he doesn’t have a high-altitude endorsement. He can’t ACT as PIC but he can log the time since as long as you are rated in the category and class of aircraft (Multi-engine land) and no type rating is required you can log the time.
You can log all of the time you were sole manipulator of the controls. Logging cross country time requires that you takeoff and land. (Legal Interpretation Gebhart – (2009) Safety Pilot)
An important sales element for use in persuading buyers was the fact that no FAA type rating was required to pilot a 425. It is not a true jet and has a gross takeoff weight under 12,500 pounds. Link
(e) Logging pilot-in-command flight time.
(1) A sport, recreational, private, commercial, or airline transport pilot may log pilot in command flight time for flights-
(i) Except when logging flight time under § 61.159(c), when the pilot is the sole manipulator of the controls of an aircraft for which the pilot is rated, or has sport pilot privileges for that category and class of aircraft, if the aircraft class rating is appropriate;
You may not ACT as PIC without a high altitude endorsement.
(a) Type ratings required. A person who acts as a pilot in command of any of the following aircraft must hold a type rating for that aircraft:
(1) Large aircraft (except lighter-than-air). [Note: Greater than 12,500 lbs]
(2) Turbojet-powered airplanes.
(3) Other aircraft specified by the Administrator through aircraft type certificate procedures.
(g) Additional training required for operating pressurized aircraft capable of operating at high altitudes.
(1) Except as provided in paragraph (g)(3) of this section, no person may act as pilot in command of a pressurized aircraft (an aircraft that has a service ceiling or maximum operating altitude, whichever is lower, above 25,000 feet MSL), …