Just curious, when did 3/8" drills come on the market? All I seem to see in the vintage drill market are 1/4 and 1/2" and that is it. 1/2" would be great if they went a little faster than 200 RPM's.
WAG, but I think 3/8 drills really became mainstream in the early 70s.
I think you will find that most 1/2" drills spin quite a bit faster than 200 rpm, even the largest of spade handles. Most are in the 350-600rpm range, and even the larger 3/4" drills are usually 50-100 over 200rpm.