strange perimeter problem

[alaris2 1]

so after 5hrs printing my first organic shape object and first time I got support to actually work.. I get this..

http://i177.photobucket.com/albums/w228 ... 000009.jpg

curiously the object is symmetric but this is the other side..

http://i177.photobucket.com/albums/w228 ... 000010.jpg

before another 5hr print, I'm trying to understand what went wrong.. I'd love to hear any theories.. so far I've got:

1) I was printing at 120mm/s - this doesn't really explain the weird pattern or inverse on the other side very well, but Joergen did mention that perimeters suffer at speed, I wonder if this is what he meant..

2) I foolishly set the print order sequence to 'perimeter loops infill'

3) the organic shape has curves more accurate than can be sliced by Cura so rounding errors lead to this effect. This might explain the vertical symmetry. I've never had anything else print with this poor quality an edge but most of what I print has sharp polygonal edges.

4) belts not tight enough, or perhaps some are tighter than others? does it matter if one side is tighter than the other as long as they all sing? do they have to sing the same note?

5) bed not level. but i don't think this would cause this effect.

love to hear your views on this subject - I don't really want to print much slower unless i have to, because 5hrs is already a very long print so 50mm/s is a whole day printing!