Just putting this in here because it's not too serious, during a Time Attack event of the Porsche Club around here, I came across a 718 on track. My tires had cooled down and I needed a lap or two to get them back up, this was on the second lap when they weren't there yet. I followed the 718 to find out how my car held up on the straights. Driver was a little all over the place, but he was also on Cup 2 tires like me.
The car in front always gets on the throttle first so it's hard to judge, but the differences are really not big. Obviously my car has the FS headers, a FS protune and, most important of all, DREAM2 exhaust tips
In terms of actual straight line speed, the maximum recorded speeds were shown on the live timing screens. This number is, however, a little dependent on just how late you want to brake.
My car: 193.9 km/h
981 CS: 189.8 (slight mods maybe, he definitely had an exhaust on it)
718 BS: 196.8
In a different session I had a 195+ km/h high but I don't remember the other cars.
Happy to see the real life improvements the mods have done to my car, as it wouldn't have been too different from the 981CS stock. Really hard to do the same on a dyno. In any case, for 2 MPH difference to 120 MPH I'll take how my car sounds.