Early 58 Barons (3 blade props) have a T/O-MCP setting of Full Throttle/2700 RPM, no power reduction required. Max cruise power on the other hand is 24.5"/2500 RPM. The same practice is applicabe to the 402Cs. Only aircraft I flew witha 5 minute limit was C206/210, from what I was told, it was a heat related thing, but never been able to confirm that.
The company I worked for had a policy that ops at night or in IMC, aircraft was to be climbed at best rate and power left at T/O until through the MSA/LSALT, which was only a couple of minutes worst case.