In reply to Pandora:
I probably worded my reply a bit sloppily. On paper you might find that a WM product will be cheaper and in some cases lighter, and so if kitting to a "weight save/price" criteria they can come in slightly ahead in terms of value. That and being able to order them from a retailer was what made me purchase one bag that I later sold and another that I have kept. I was very happy with both.
In terms of comparing specs: I don't think PHD use the EN type of standardised ratings for any of their bags or other products (their down however is rated to the EU EN spec.) but my experience of a number of pieces of kit is that their quoted "typical operating range" is conservative and outperforms above what you might expect. If it is anything a bit unconventional like a halfbag then their descriptions of what you might be happy using it for (e.g. 'proper overnight good sleep' compared to bivvying til pre dawn start) are very reliable IME.
The PHD stuff I have got in recent years has all been 900 or 1000 FP stuff. This is the best you can get anywhere. And it leads to very, very, compressible kit as well as being light. In turn this might mean you can possibly drop down a pack size and save further weight if you look at pack-ability of all kit in addition to weight.
Be aware when trying to compare offerings from data sheets is that when you see WM specs the US measure of fill power is used. It is a different method but most testing shows that the WM kit uses down that exceeds its rating. Net effect is it is probably slightly inferior but perhaps not as much as you might think by just looking at the numbers and translating for the different standards.
If I was buying anything now my main thoughts would be is it warm enough, will it arrive in time, is it light enough, will it have a good resale value if it is for a specific trip. Both brands will meet these criteria extremely well. PHD comes in ahead on all the technical stuff, though some products can be purposefully minimalist, but you pay for that and have to wait for most things. If it was something I could see myself using until totally trashed it would swing me even more towards PHD even if the additional cost was significant. As well as being technically slightly superior the fact they are in the UK is great for repairs.
Also I'd not hesitate to pick up either brand's stuff 2nd hand if it suited requirements. They are both "premium enough" of a brand that they have likely been stored well and so on. Another good place to check is the bargain page on PHDs site. It's kind of hidden away but you can sometimes find something that is perfect and readily available from them. Also, the occasional special ranges that they do can also work out quite a bit cheaper in some cases.