When I bought my machine back in 1989-90. I didnt know anything about industrial sewing machines or clutch motors. It wasnt until a few years ago I discovered they make two different speed clutch motors. One is 1720/1740 rpm, this is for heavy duty upholstery work. The other is 3460/3480 rpm and is used for light weight garment/sail making. My machine had the 3480 rpm clutch motor and it was like sewing with your sewing machine powered by a top fuel dragster engine. It was very hard to control and sewing straight lines was nearly impossible.
The new SQ5000 powering my Adler 267 is pure luxury. With the 50mm pulley I dont have to use the hand wheel to start or to stitch slow enough around tight corners, and it is still fast enough to sew long straight lines.