Ian,
The PHD sleeping bags are slim. The Ultra bag for example would fit perfectly inside the Alpkit PD800 and still have plenty of room to loft, probably not dissimilar to the design and intention of their Combi bags.
The vests are sized to go over a base layer and fleece so are quite roomy. I was similar to you in that I’m a measly 38″ chest but 6′ tall and went for the Med based on chest size. The fit is perfect, it certainly isn’t too short and chest size is spot on. It has loads of loft though so even in just a base layer it fills the voids to stop heat loss and the pits are slightly elaticated too.
The Minimus vest always seems to appear in their sales for £89 (keep in mind their £10 delivery!) although IMO at £125 it’s still worth the money compared with the similar spec. OMM Finch. Also it looks a lot nicer than in the photos. The Rab Microlight is similar weight and packsize but certainly won’t be as warm, but then it’s cheaper.
I suspect the 900-fill Ultra vest if anything like the sleeping bag won’t ‘feel’ as warm or cosy due to the lack of sheer bulk. More of a performance layer than a cosy cuddly down warmer 🙂
I notice Terra Nova have more lovely new kit this year, I’m interested to know if their 900fill bag is EU or US measured down, it’s still colder and more expensive than the PHD Ultra!