I remember thinking the T1 that lit up my entire school district was insanely fast. That was until I went to college and found they had a 2Gbit fiber optic Internet2 link on campus. That was mind blowing.
My memory was marathon on the Mac played over a similar connection speed. I forget the software but it allowed a networked game to be emulated over a PPP dialup session.
Doom was ok over dial up computer to computer. Quake was even slow connected direct over modem. I would guess the slowness was the extra data for the 3rd dimension going over the wire.
I have never, ever seen pings as low as the ones I've seen 15/20 years ago when playing online.
I remember when I played Counter Strike 1.5 or 1.6 on a 10 MBit fiber which was very new at the time and pinging on servers nor far my house (few miles) even sub 10 ms. Those were numbers that competed with lan servers over ethernet.
Nowadays I have a much better connection, and yet, I rarely see myself with such a small latency anymore, it's at least twice that.
I agree about the big comercial servers/games. The community driven servers are often better latency, e.g. I got 7ms in this game, the same server was 60ms when gaming through the VPN and enterprise proxy.
Oh man, I remember the good ol' days, when a 1.5 Mbps connection was unthinkably fast. I imagined only God herself had a T3.