In reply to ablackett:
> (In reply to lithos)
> [...]
>
> I read somewhere that anything above 650 was a waste of money because the weight of the outer is heavy enough to squash 800 down, down to the size of 650. So you loose the extra fluffyness.
I've heard this and I agree, somewhat. I don't know about it being the weight of the outer, though that might be part of it with some models.
I think just generally sleeping bags, getting compacted and pushed and pulled and squashed and used in the damp and in crowded tents, or sitting up in a bivi etc are often used in non-optimal situations in terms of down distribution. I've no doubt that 800+ down lofts nicer and thus insulates better than 650 when they are laid out in the shop or factory, and is lighter. I have several 800+ bags, used in Antarctica, AK, Karakoram, Tibet, Andes etc. and I'm not about to replace them with a 650 bag for those places.
Only my personal opinion, but I think for having a decent BC or higher camp in a very cold place in a proper tent, then an 800+ bag is worth it. It will be able to be used 'as it should'. For many actual climbing situations, or places less cold, I think the benefits of the 800 will be lost somewhat and a 650 will be fine.
I have a PHD Minim 400 and it's a nice piece of work, but without Drishell I worry about it getting damp, or torn, so it's not very robust and often I find myself not game enough to use it, opting for something a bit less quality but more utilitarian. You won't sleep well if you're constantly worrying about the state of your sleeping bag.