I've driven at around 100 mph for about 2 hours in my 84 300D (turbo). Very comfortable, smooth and quiet except for engine noise. That was soon after I bought it, and I rarely go over 80 anymore. 80 feels just about perfect in mine, any slower and it feels too slow, any faster and it feels to reckless. I don't know anbout anyone else's W123, but mine doesn't pull emergency maneuvers at speed too well!