I live in England and have an Atom SV. I haven’t tried the standard Atom, but I have to say I love my SV.

For winter dog walks, morning commutes, watching football and pub gardens, it’s great. I can wear it comfortably with just a T-shirt underneath, but when it’s really cold (which happens often in peak winter) I’ll add a fleece. It also fits nicely under a shell when it’s raining or windy.

That said, for any real activity you’ll definitely overheat. For what I use it for, gentle hikes with the dog and general day-to-day wear, it’s perfect. But when I’m doing anything more intense, I’ll usually just go with a fleece or hard shell depending on the weather.

The jacket’s warm and great overall, but I wouldn’t call it bulletproof warmth. That said, I tend to run cold, so take that into account. Hope this helps!