No way a 40+ years old can compete against the modern pro. Sampras can compete on the senior tour. Unless if he was playing in the 60s when it wasn't that competitive, then it's doable since Pancho can still compete despite well past his prime.
Tier1(goat): Federer; Tier 1.5: Laver, Gonzales, Sampras, Nadal, Borg;
Tier 2: Lendl, Connors, Rosewall, Tilden; Tier 2.5: McEnroe, Agassi