Reporting back, with a slightly off-topic follow-up. So...

I too have been running w/ Marlin 1.1.0RC5 with printbus' config settings. Two main observations:

1. The primary advantage to this has been the preservation of overall print quality at higher speeds. So on that basis alone: "win".

2. Slight, but repeatable improvement of issues I associate with retraction problems. I THINK this was the result of the improved z-lift performance (in addition to the more aggressive extruder jerk settings).

I did play around with cooling a bit. The first experiment was with "fine-positive-features". About the only thing cooling did was exacerbate some spider-webbing. Tried a couple of different approaches, but no real improvements.

Inspired by something in another thread, I decided to try printing "the cube" with 0% infill..., i.e., hollow.

FINALLY..., a scenario where cooling actually made a demonstrable, positive difference! (a first for me)

The layer times with a hollow cube were so low, that when the head advanced to and printed the next layer, the previous layer had not cooled sufficiently to support the new layer. The problems were most visible at the corners.

Increasing layer times by adding back infill OR turning on the cooling fan solved the problem.

The frustrating thing about the fan is that it is a rather blunt instrument. It is difficult to generalize and generate parameters that actually create intelligent, reliable use of the thing.

With "fine-positive-features", I assumed that dwell time on the tiny spires was a problem that the fan could help. I was imagining exploring the idea of driving the fan based on some kind of analysis of inter-retract times. Not sure I'll play with that or not, given the negative results I got with several different fan settings at a gross level.

On the other hand, the fan SEEMS to be very useful for thin-walled layers with rendering times under 10-15 sec or so. Not quite sure how I'll generalize this..., but it's something I'll keep in mind.