Just to add more perspective to the guys, you only need enough octane to keep the engine from knocking, any more than that and you don't get the benefit of the additional octane rating. More than c.r. is involved. Generally it's all the factors that relate to heat of combustion that will drive octane requirement. Air temp, load, timing and so on all contribute to the outcome. At break in you won't have much load on the engine. Depending on whether you fire up in a heated shop or outdoors may change charge air temp. I could go on, but you probably get the point. Now, all that being said, you're doing a break in procedure, with a bunch of unknowns. Covering your butt with "too much" octane rating is one of those safety factors that doesn't cost much if anything at this point. So I'll join Mike and Richard since it's the safest advice given the knowns. It's later, when you're in mortal combat on the strip, that optimizing your octane rating requirement becomes more critical.