Originally posted by VTECnKEN
Metals have an elastic memory that eventually tempers into a solid and ungiving shape. During a break-in period, if an engine is constantly run at 35mph, the metals will stretch/compress into shapes that provide the least resistance for the given operating parameters. After the break-in period, the engine will operate at optimum performance in the 35mph area. If one were to look at a dyno pull, you would be able to see a slight power fluxuation at a certain rpm, vtec aside, this rpm would coincide with the rpms required to move the vehicle at 35mph. If you compared two identical cars that were broken in at different speeds, one at 35mph, and the other 70mph, the car broken in at 35mph, driving at 70mph, would get less power/gas mileage than the 70mph broken-in car. Likewise, if the 70mph engine were cruised at 35mph, it would get less mileage than the 35mph engine would. However, in a world that involves constant acceleration and varying cruising speeds, the best thing you can do is to cruise at the same exact speed on the highway. Surface street traffic isn't static enough to provide any good break-in time, however, on the highways there is enough time to just cruise at a certain speed, say, 65mph. During break-in as well as during the rest of the engines life, be wary of bringing any engine into the upper powerband often, even on a Honda. Take a 5 year old engine that's been revved to redline about 100 times in its life, or 20 times a year, and the same engine, same age, that's been revved to redline 4,000 times, or 800 times a year, and you better believe that the latter engine will have less power! If youve been persistant enough to read all of this, thank you for reading, and good luck with your brand new engine/car! 
Damn. That's some good info. Thanks.