I use fabrics n stuff regularly and have made down underquilts from their fabric.
I use their pertex 4 as its water and dirt repellant and highly breathable,at a slight weight penalty.
I'm not sure on that exact fabric, but I'd echo the concerns of breathabilty. A dwr or uncoated will be more breathable and these are rare on fabrics n stuff at the moment.
I'd go to ebay and check out ripstop on there. Sometimes you can pick up pertex microlight on the bay which IMO is about as good as you can get for both of your quilts, being downproof and teflon impregnated.
IME, treating uncoated nylon with nikwax does a fantastic job of adding water repellancy and can easily be retreated. Might save you some pennies.