I'm a 10.5 on a brannock and am sort of in between a 9.5 and 10 on a viberg 2030. The 2030 is just a little narrow so I believe in the 310 I would be a 9.5, but I've never owned a pair.
Thanks everyone for the advice. I reserved a pair in US 10 (my standard size) and feel, I shouldn´t worry about the boots being too small. I usually play around with socks and/or insoles if I have any issues, so this sets me at ease on a EUR 1.000 boot...