I don't remember writing "You're a peach," and probably wouldn't say that today. "You're a delignt" might work. So would "You're a great leader," of "You're an inspiration." This e-mail is short enough that it would make a great handwritten note. When time permits, choose the handwritten option.
To: Calvin Burkhardt
Subject: Thanks for Breakfast
Cal,
It was great fun seeing you yesterday . . . especially nice since we're both so darn time-challenged. Remember the good old days of 60-hour weeks?
I'm glad to hear you're busy and happy, and that your family is doing well.
You're a peach,
:Bill