The 99 NB I have develops about 200-220HP at 9.5-10psi when it is tuned to do so. Normal tune for daily use limits the engine to 160-180. (Stock internals, etc.) Due to cooling issues, sustained high speed above 100 is not the best thing to do. The 99 will easily reach gear/RPM limits when it is tuned to do so. (And the gear limit is slightly higher than stock, due to a different 5th gear ratio.) A front air dam, side skirts, and a cooling scoop, along with an effective oil cooler would make a big difference. Unfortunately, the state laws in my area have gotten draconian concerning speeds 20 or more over the limit. Somebody decided that average speeds of 85 on the Atlanta area interstates were too high, given the poor mechanical condition of many Atlanta area cars. Besides, the state and local governments are getting desperate for cash any way they can get it.
As to the autobahns in the 70's--someone was always going faster than you were. There were at least two very high performance sports cars in the local area (Trier, Bitburg, Eifel area, etc. that commonly were well above 120mph when noticed on the autobahn. One was a Ferrari, and the other a German made mid engine car with no obvious makers mark. Of the two, the German car looked like speed incarnate, even when parked. It may have been a prototype, or a custom build, I never found out the details.