And remember, there are different types of 'cold' - dry cold or damp cold. Here in the Highlands of Scotland, it's not the overall temperature you need to worry about, but the real-on-the-mountain temperature when you factor in windchill and damp. And, no matter how good your sleeping bag is, if it's filled with down, it will lose insulation when wet. Keeping kit dry in a tent when packing and unpacking in the p*ssing rain on a mountain far from home is a skill in itself...!
As for camping on snow - there are endless types of mountain snow too - hard packed from mountain freeze / thaw cycles, hard-packed with a damp sleety top-layer, soft unpacked which is a bugger to pitch on etc. And the joys of freezing tent pegs etc.
However, lest this all become too gloomy, the rewards as you rise from your tent at first light on a sharp morning high up a mountain outweigh hardship and make you forget all those trips where you wake up miles from anywhere, heaving rain, wind blowing a hooly, in thick mist
My overall feeling is that it's a little futile to offer opinions on suitability of gear etc from the comfort of a comfy seat indoors, another thing to wild camp high on the mountains a few times, find out both how miserable / rewarding it can be, then start working out what kit best meets your own needs based on your experiences...