Assuming its my company and we're a small outfit I'd love to have them but I wouldn't pay 3x (or even 2x) overhead.

1) At a 3x salary you'll need to lose two other employees and sacrifice the redundancy, idea mix etc that you point out. Reducing the HR etc overhead by two employees is far less of a gain.

2) Their higher output is going to be at least partially due to more intensive work habits which may not be sustainable over the long run.

3) If they ever decide to move on you need to hire three replacements and hope they work out and can take over from your superstar without losing too much momentum (all without ever meeting the guy since its unlikely you'll find & hire them within his two week notice period).