Printing with colorfabb XT fails after several successful layers
This looks a lot like under extrusion caused by heat creep.

Heat creep is when the nozzle temperature 'creeps' up through the filament and makes it melt (a bit) and form a blob (or just widen enough to get stuck) a centimeter or two before the nozzle.

The characteristic is usually that everything works perfectly well for some quite fix amount of time, then there is severe under extrusion.

Solutions:


Lower the temperature (yes, as then the heat won't creep as much!)
Add a fan cooling down the cooling part of the print head


I have the same print head as you it seems (E3D 1.75 all metal) and I had heat creep when I changed the fan to a less noisy one (but also less effective).