ENGINE BREAK-IN GUIDELINES (from an old fart that has been building engines for decades).
Regarding engine break-in, there are some specific rules to follow regardless if you are riding a cast-iron or aluminum (alloy) engine. Reduced RPM and the avoidance of cruising RPMs are critical, regardless of speed. Breaking in an engine by around-town driving is the best option, with its varied engine speeds and stop-& go situations. Although recent engine designs are less susceptible to improper break-in it definitely remains advantageous to keep RPMs below 3000 for the first 5000 miles.
Another important factor are oil changes. Because engines come from whatever factory with whatever oil in it, it is best to change the oil after 1000 miles to whatever grade and brand an owner determines is "best". From that point forward, it is best to change carbon-based oils (made from dead dinosaurs) every 3000 miles, while synthetic oils will lubricate an engine effectively for 5000 miles. Quality is paramount!! Many brands are available, but the continuous winner in Consumer Reports reviews is Valvoline. Because I am a sucker for scientific proof, I run synthetic Valvoline in all my vehicles other than my Harley-Davidson (I run their synthetic oil while the bike is under warranty), and the extra cost of running synthetic oils is definitely worth the expense.
Lastly, let me mention that old engine designs require much more attention to engine break-in. Iron block Royal Enfield classics for instance, are much more susceptible to engine particularities (rarely to an owner's advantage), while also requiring a higher level of maintenance than the newer alloy counterparts..