I know Trevor Tarring drives his Frazer Nash at 60-65 mph — I followed him once and was most impressed, but Nash drivers tend to cruise at maximum speed, a splendid tradition and long may it last.
When mentioning 45 mph in a general way as a cruising speed for Vintage light cars I was thinking more of the sedate type of Frazer Nash with running boards and a tall windscreen; the screen on my own Nash absorbs a surprising 7 hp at 60 mph. Actually, it cruises just above 50, largely due to the 3:1 top gear exceptionally high even by F/N standards.
Modern cars seldom need to rev above 3000 on regular roads thanks to fifth gear. Consequently if we admit that there has been some faltering progress in the last 66 years, then 2200 would seem appropriate for cars built only 25 years after the dawn of the industry, resulting in quite a moderate cruising speed.
For relaxed cruising Trevor would like my 1700cc 2-cylinder G N, restored, sorted and adjusted for 60 at 2000rpm even without its intended 2 1/2: 1 top gear. It makes me wonder why Alfa Romeo decided on 6 cylinders for their famous 1750: cold starting perhaps?