Graham,

At the temperatures you mention, a regular kilt is just fine-the key areas are head, ankles, wrists and stomach-all catered for by wool hose, kilt and bonnet-you can sort out wrists.

The advantage of kilt over trousers is that a bubble of warm air is trapped under it and withing pleats-super insulation.

The knees never seem to get cold so you will be fine.

The only snags can be if there is a high wind chill factor--then you might need four hands--there is no need to draw a picture!

However the hat is essential-something like eighteen percent of heat loss is through head-and at temperatures well above those you mention-no hat is a risk factor.

Also remember climbers trick-keep toes moving-that keeps circulation going.

James