GGG? i'm a big fan of his, but his success has never depended on hand speed his success is due to timing, measuring/judging distance, balance, and punch placement
Mike McCallum wasn't the quickest, especially after he rose to 160. Carlos Baldomir managed to win the lineal welterweight title, but was one of the slowest world level fighters I have seen (without much of a punch either). Julio Cesar Vasquez won a 154 title twice and beat Winky Wright, but had very average hand and foot speed.
Tito Trinidad looked a bit slow vs Hopkins, and Hopkins himself wasn't particulary fast handed for a world class fighter.