The Lear 45 is certified to 51,000 feet, it's what I fly for a living, there's no way I'm taking it there! Just because it's certified doesn't mean it's safe, all the conditions must be right - most of the time in the case of the 45 you'll stall before reaching 51. You must know your aircraft's limitations. It's sad two people lost there lives over this.
BG, ATP-Lear 45, Falcon 50/2000