When the 030, and the 031 that followed were current - they were one of the fastest running saws Stihl sold. Also one of the most reliable. The bigger 040 and 041 ran slower and had more problems.
For the homeowner, farmer, and firewood cutter - the 020, 030/031, and 040/041s were our best sellers.
The only common problem the 031s had was the ignition condensor. Often died early and had to be soldered in.
041 was prone to many other "nuisance" problems. Impulse hoses breaking,intake manifold gaskets getting sucked in, and oil-pumps leaking into the crankcase.
Back in the days of the 030 and 031, just about any saw Stihl sold with an upright cylinder was fast (030,031,045,075, etc.) -and the ones with horizontal cylinders slower (040, 041, 041G, 050, 051, etc.)
The O8S was an exception with a upright cylinder but very slow cut speed. That's because it had a governor on it.