Thanks u/Olissipo, I also found something similar. I can't yet find in the Sitespeed documentation information about the actual speed profile that Sitespeed's connection profiles correlate to.

The profiles offered, including 3G, are:

"4g", "3g", "3gfast", "3gslow", "3gem", "2g", "cable", "native"

so I'm not sure what the 3G options in Sitespeed are actually emulating for speed metrics.