Hi John,
I wrote an article on this subject for the VW Club magazine back in 2009. It tells about the formula to work out road speed from RPM (you need to know the tyre circumference, gear and diff ratio), with at least a dozen examples listing their km/h per 1000 rpm, and inversely their RPM at 110 km/h.
To summarise:
VW 1200 - 29.7 km/h per 1000 rpm
VW 1500 - 31.4 km/h per 1000 rpm
VW Superbug L - 32.01 km/h per 1000 rpm
I didn't work anything out for the New Beetle, as it's a Golf underneath. But I did work out a few new generation models:
VW Mk2 GTI - 33.2 km/h per 1000 rpm
VW Mk3 VR6 - 38.8 km/h per 1000 rpm
VW Mk5 GTI - 41.6 km/h per 1000 rpm
You can't really compare the old four-speed air-coolers with modern VWs, with their five-six or even seven-speed boxes and totally different engines. Nice to compare though.
BTW - you can't buy a 1.8-litre New Beetle now. The only choices are the 1.6 (sedan) or 2.0 (cabrio). I'm sure I have the brochures somewhere and could work out their 1000 rpm speeds if needed. But they would be about the same as modern Golfs.
If you'd like to read the article, go to
http://www.vwwatercooled.com/mag/2009/2009.html and download the August 2009 issue. Enjoy!