It was -3 on my way back from work in Edinburgh and it felt pretty cold. Got used to the weather here and if it's not raining it's good enough to ride, wind and low temperatures doesn't really bother me, as riding in fair weather only would limit the riding time as it's always something (however the summer had some nice sunny weeks).
TJ is the Pentlands mud all nice and frozen or still wet?
Can it be -5 outside and still wet?
Cold strong wind can make a ride miserable but it all depends who are You riding with as it's always better to ride with some friends, when I'm out riding with my mates the weather doesn't bother me even more 🙂