TRUE OR FALSE: Riding one frame size smaller with more spacers/longer stem is faster than riding the ideal frame size
This is generally TRUE. Smaller frames typically have less drag (this is generally around 2 – 3W (45km/h) per size step). This is because the overall frontal area changes from one size to the next.
We would not recommend getting a bike that doesn’t fit you, because the most important is to be comfortable so you can actually hold an aero position for long periods of time. But if you are on the cusp of two sizes, and most importantly you can achieve the same ‘optimal’ position on both bike sizes, the smaller frame should save you a couple of watts.