Motors are designed to be run. Don't be afraid to run them. All the Yamahas that I have had will cruise best between 4600-4900 rpm. I will pick up a little better fuel economy and loose speed between 4-4500 rpm, but I feel that they just run better at higher rpms. My friend who is also a yamaha master mechanic agrees with me, and always tell me don't be afraid to run them. He says that he sees more problems in engines that have most of their hours under 4000rpms. He also tells me that the newer yamahas are designed to run at 5000rpms. Its also good to open them up every once in a while and go full or close to full throttle. That being said I have only run 3.3. and 4.2L V6's in Twin applications and have a fishing buddies who runs 350's. The smaller 150's maybe different, but maybe not.