I have the old ME Lightline (the blue 550 model, not the green 450 model).  With ME, I think the number refers to the weight of filling, so it should have a comperable fill weight to the Xero, both have 700 fill power down so should be quite comperable.  Mine was rated down to -12C, but I don't think I would like to sleep that cold in it.  I've used mine down to about -2C and it is fine in tee-shirt without getting anal about closing baffles etc.  I like quite a bit of warmth (but hate being enclosed in baffles etc), so others may well find it suitable for lower temperatures.  In summer it is way too hot, anything above 10C and you need to completely unzip it and use as a duvet, hence I've bought a Marmot Hydrogen for summer use.

Except on a very light bag, I would want a full zip for the extra flexibility, so for me, a 3/4 zip would be 1/4 too short.

I like the elastication on the ME bags. They hug you without feeling restrictive.

Jasper

be careful of the length you will need.

standard is for up to 6ft 1in, some websites say they are 1 size but they come in standard and xl.

There is a somewhat short review here on OM.

www.cumulus-sleepingbags.co.uk   are worth having a look at, i've just bought one so i won't be boring everyone with my bag quest any longer