Aye Up All,
I've owned both for several years. (Size XXL - the jackets not me)
I deploy 3 + times a week - out all day, rain/shine, often spend hours laying up.
I used the PCS lightweight (585g) (Thermal!?) smock (£25 version) for one season and it was almost immediately relegated to the back-up bag in the garage.
I found that it hardly made any difference at all re heat retention and with some base layers it felt restrictive especially at elbows and shoulders even though I had purchased a size with room to spare.
Despite the additional pack size and weight of a Buffalo Fibre pile I went back to that for a short time for the better performance.
The mil 'Softie' version (£49) however has proven well worth the extra brass (and weight @785g) and the (negligible) extra pack size.
I've put it on after a mornings tramp around the sticks when carrying a ruck normally leaves a damp patch on my back which chills quite quickly - no probs with the softie - keeps me warm over mid day refs break, seems to be good at moisture transfer too.
I've laid up on obs in a hooped bivvy for 8 hours at 5 - 8 degrees C with it on and was comfortably warm.
I've recently used it (end of Sept) and a pair of the old olive/sand thermal trousers instead of a sleeping bag and kept warm right up until the pre-dawn chill. Up and about for 5 minutes and I was toast again.
The only improvement that I could add to it would be elbow-to-wrist patches to keep that part dry and to protect the material from scags as the outer is only lightweight material. (avoid sparks!)
andyragg - re the colour olive (a favourite subject of mine) - If you think of all the colours that the olive fruit
can be, that of the PCS thermals does fit in there somewhere - but personally I would also describe it as nearer to khaki than what most would think of as olive green. Interestingly in some conditions when viewed from a distance and you can't see the pattern of MTP, it too comes across as a sort of khaki - very effective.
If only we would adopt the RAL colour chart!!!! That stated perhaps we only need a colour chart covering the so called 'earth' and mil surplus clothing colours - a dedicated BCUK
Rural
Colours
Palette?

I might look into that.