As MG says, OPTIMUM is just that. When OPTIMUM is closer to 370 than 330 - then climb, not before, unless there is a very good reason like weather/terrain or trying to 'bag' a flight level - assuming you have done the step climb fuel extra v. cruise savings x time-to-go check, plus taken the wind into account. FMC 'step climb' point does NOT take fuel economy into account, it is purely weight based (737).
Again assuming you have taken into account ALL the factors regarding max altitude from your paper tables (eg ISA dev etc as the FMC does) AND your company operating licence ALLOWS you so to do, then climb outwith VNAV to the level you have calculated as safe. Some FMCs have a cruise C of G option which can give you a higher 'max' level but may NOT be approved in your ops manual.