The reason why I was looking at the Phantom is because I have been using the MH Lamina 35 and I love it. I figured if I like my synthetic MH bag, why not get a down bag by MH. I've been looking at comparison's since you mentioned the WM and Montbell.
MH - 1 lb 7 oz, fill weight 11oz $305
Montbell UL SS 3 - 1 lb 8 oz, fill weight 11oz $299
WM Summerlite - 1 lb 5 oz, fill weight 10oz $330
FF Merlin - 1 lb 9 oz, fill weight 11.5oz $329
To me, they all seem like the same bag. Well except that MH is a "mainstream brand". I live in Denver so I could easily get to Boulder to the Montbell store to get the UL if I wanted. And I might actually go check them out. The WM and FF I would have to order which pretty much puts them out of the equation because I don't deal with online ordering when it comes to sleeping bags, shoes, and up until now packs (I'm going to give ULA a try). The MH is right here in Denver at REI. Best part about that...if I hate it, which most likely won't be the case I can just take it back.
Edited the weights of the bags.