I don't mess with the extrusion multiplier.
leave it at 1 (100%)

Printing too slow can have it's own problems. And fast travel speed is not a good idea either.
what are you printing with abs or pla ?

I do most of my printing with pla at 210c and 65mm/s print speed. With travel moves also at 65. Keeping the print head moving at the same speed removes the shake and spikes you get with sudden travel accelerations.

If I'm printing a little slower - say 50mm/s - then I'll often drop the temperature down to 200.
I also usually print at 0.3mm layer height. I'll go down to 0.2 for stuff that needs more layers for under hangs or overhangs or vertical curves.

The idea is to balance the viscosity of the filament and the speed it can flow, while maintaining a fast setting.
I have print area cooling fan on all the time.

I did mess about with retraction setting a short while ago. And eventually went back to simplify3d's default. Which are 1.8mm distance at 40mm/s speed.
Gives me the cleanest prints with the least amount of stringing (none, essentially).

I think people get over complicated and once you start messing about with things that didn't need to be messed with, it's a slippery slope.