The troublesome printer is a hybrid Wombot Exilis and Gmax 1.5. I call it the Wogmax. Uses Ramps and Marlin 1.1.0-RC7
I have done the calibrations needed, eSteps, extruder, PID, stepper current etc and then rechecked. Dimensionally, prints are very good. It has no slop, z is very good, belts and tight.
Its using an original J-head 0.5mm. I've only been printing with PLA on this one.
I've tried print speed changes, layer height, extrusion multiplier, temperature, while they vary what happens they don't stop it. At the moment extrusion multiplier it is 1.2 for PLA. I've tried Auto and manual. Fan on/off. I confirmed the nozzle is 0.5mm.
Initially I thought it was humidity affected filament. I've tried 2 other new out of box brands and get the same finish.
One strange behavior is that at very slow extrusions I can see the filament "spits" occasionally. Increasing the rate stops it.
While the finish on this big rook looks kind of cool like a stone texture, it isn't right. Kind of like over extrusion and moire. Its like its over extruding then underextruding cyclically very quickly. In other words pulsing. This seemed to be a driver current problem or stepper issue. I adjusted the current and replaced the stepper. Still the same basic underlying issue exists.
Doing calibration cubes, not one looks right. They are layer true and straight, but the finish is not as good as it should be, maybe I expect too much.
The Gmax extruder uses a fixed spring for extruder tension. Perhaps this is too strong. That about what's left. I'll post a couple more pics for comparisons.
... I solved it initially by replacing direct drive with some geared extruder and later on moved spool on to bearing supported spool holder (so it rotates smoothly) and a ptfe tube between exit from spool holder and the extruder itself (seen that trick on UP!Plus2) this way position of the extruder does not affect in any way the force required to pull filament off the spool ... 
