Actually 10w60 flows better than a w30 in cold temps. It is a special oil blend.
See this comparison table:
Cold Crank Viscosity in cP (Centipoise)
Castrol Edge 10W60 - @ -25 DegC
4860cP
Millers CFS 10W60 @ -25 DegC 7000cP (Most 60 weight are around the 7000cP
Millers CFS 10W50 @ -25 DegC 7000cP
Silkolene Pro S 15W50 @ -25 DegC 6800cP
Silkolene Pro S 5W40 @ -30 DegC 6500cP
Edge Sport 0W40 @ -20 DegC 5850cP
Silkolene ProS 5W30 @ -30 DegC 5000cP
Castrol Egde 0W30 @ -30 DegC 5800cP
Reference thread here:
http://forums.m3cutters.co.uk/showthread.php?t=41680