Managed to sort out my problem. Almost too embarrassed to tell but.. as it turns out it is not wise to calibrate machine axis with a dial indicator. At least a machine that has not super accurate ballscrews. Also the testpart that showed inside measures correctly and outside wrong, was coincidence I believe. I re-calibrated my axis with a 300mm caliper. Problem solved.

So anyway here is a little cherry on my strawberry cake:
Material: S335
8000rpm, 350mm/min, DOC 3mm, 2-flute TiAIN 6mm endmill.
Some chatter but nothing major... Shitty workholding. Nice blue chips where flying :)

Click image for larger version.  Name: pilt101.jpg  Views: 417  Size: 87.0 KB  ID: 23858

Click image for larger version.  Name: pilt102.jpg  Views: 458  Size: 129.4 KB  ID: 23859

Click image for larger version.  Name: pilt103.jpg  Views: 466  Size: 199.4 KB  ID: 23860