I was told keep it under 4k for the first 1200 miles. But the issue is controversial with some saying aggressive driving is good early on to help seat the rings. One thing both camps agree on is it's best to vary the RPM throughout the break-in period --e.g. don't turn on the cruise control at 2700RPM and leave it there for a three hour drive.
(edited "very" to "vary" to avoid looking like an idiot
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