Is a slower outer perimeter speed still meaningful?
Lowering speed on outer perimeter has always been mostly wrong, but possibly useful. Usually, it's a poor approximation for what you really want to do, which is lowering acceleration on the outer perimeter, to avoid surface quality and dimensional accuracy errors due to ringing and backlash. However, on bowden printers without compensation for pressure (&quot;linear advance&quot; in Marlin, aka &quot;pressure advance&quot; in some other firmware), slow acceleration and high speeds give really bad error in extrusion consistency, so you're better off just lowering the max speed too whenever you lower acceleration.
It's also possible that you may want to print at extremely high speeds for inner walls and infill - speeds so high that you get a lot of extrusion consistency problems. If so, it would make sense to retain a sensible max speed on the outer wall. This won't avoid the part strength problems from printing too fast, but if your models are just decorative, it might be worth it.
Generally, though, I'd recommend solving these problems right (using linear advance if your printer needs it, lowering outer perimeter acceleration to get rid of artifacts, printing at a speed your hotend can handle, etc.) and deem &quot;slower outer perimeter&quot; an idea whose time has passed.
Also, note that if you're using a bowden printer without linear advance, sticking to the same speed for all extrusion will largely paper over the problem. This is probably the source of your observation that it &quot;improves print quality&quot; for you.