Tennis balls used should be equal in bounce, air temps certainly close enough.
That "100mph" thing is tough to quantify without a radar gun. I do know the past No.2 for Harvard U, Aba, stood about 5' behind the baseline to return my first flat serves, and stood 2' inside the baseline to return my second serves in the doubles sets we've played.
The local SanPablo court A/Open winner also stands about 5' behind the baseline against my first flat serves, but he only moves forwards to maybe baseline position to return my second serves.
I stand about 3' behind my baseline and return all their first serves, and usually just atop the baseline for their second serves.
And they block back my first flat serves, not taking even a 3/4 backswing.