I don't think the multiplier is meant to be set to anything other than 1.0+-1.
I think it is 0.6 by default for historical reasons because Solidoodle used a different nozzle diameter back in the day and didn't know Slic3r very well.
The Extrusion multiplier setting allows the fine tuning of the extrusion flow rate, and is is given as a factor, e.g. 1 means 100%, 1.5 would mean 150%. Whilst the value should ideally be set in the firmware it can be useful to test slight changes to the rate by altering this value. It varies the amount of plastic proportionally and should be changed in very small steps (e.g. +/- 0.05) as the effects are very visible.
http://manual.slic3r.org/simple-mode/simple-mode
Of course changing the nozzle diameter to higher value than your physical nozzle will result in more plastic being pulled in, and then you'll need to "fix" that by say lowering the extrusion multiplier.
But just don't raise the nozzle diameter in the first place. It won't work any differently as far as I know.
As for what I'm seeing, it could be
1) Filament tangling in the roll.
Try this: https://www.youtube.com/watch?v=_JQKn95512M
This would prevent the motor from moving for a short time and cause few step skips.
That , or the roll doesn't rotate easily on the spool for whatever reason.
2) X motor getting hot in few places and skipping
3) motherboard getting hot. unlikely I think for a SD4.
4) unlikely to be a zwobble on the very top layers. but it does look like zwobble on some layers.
Zwobble is more of a problem with the Z axis, not the carriage.
http://www.thingiverse.com/search?q=sol … le&sa=
It doesn't seem to be like the hotend melted anything. To me it just looks like the X offset shifted from step skipping and some filament had nothing below it so it "melted" down a bit as it does at big angles with no support.
Your bed adhesion is decent at least.
Oh wait, its an Mk2 
Solidoodle 4
