I have never notice the AI cheating on speed either.
Two areas where it does cheat though are:
1) Knows what you have researched.
2) Knows how many ships, planets, researched projects etc that you have in order to determine if you are a MEE (mega-evil empire).
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Know thyself.
Inscription at the Delphic Oracle.
Plutarch Morals
circa 650 B.C.