yeah- I really woulden't recommend this mod- personally shocked that it works- but it might be the high temps that help-
The reason I woulden't recommend this is due to the fact the whole hot end is not optimised for 1.75... when extruding it would cause a type of blooming effect- and retractions most likely will be effected negativly -
on the other hand- if you replace the hot end and extruder to systems designd for 1.75- you extruder will work less hard- and there will be less weight on your hot end for higher quality movements in theory-But also in theory- 3mm fillament has lower diameter error per extrusion so- its really a strage trade off that will probably land you back where you started in terms of quality-
If i were to design the ultimaker- id probably design it with 1.75 bowden - simply because you can just buy tight tolorence fillament and run the extruder motor at almost half the current.