I once ran a 6km test in Pirkkola in -16'C and after that got such a high fever that I couldn't even walk to the toilet without fainting... Since then my limit for fast running trainings has been -12'C or so. I just find it too cold for my lungs... Luckily there is Liikuntamylly (I'm going there tomorrow). :)
I think this is going to be a rest week for me... Let's hope that the next week will be warmer!