What are your thoughts on this for a top quilt?

I have no experience with down. What temperature rating do you think this would have?

Found this bag at Walmart on Clearance. $64. It had some good reviews. Check your local Walmart.
Sleeping Bag

I think having a sleeping bag has the feature of being able to stick your feet in the bottom. With just a comforter I'm not sure it wouldn't slide around on you. I use a down mummy bag upside down and really i see no need to invest in a proper topquilt.

I was concerned about the white cotton exterior and how that will pick up dirt, pine needles, etc. Duck feathers? I am more familiar with goose down but what do I know. And without a thermal rating it is a big guess. I would rather pick up a military poncho liner for that money and I know they work very nicely in summer months.
I like putting my feet in the foot box of my sleeping bag and using it as a top quilt, also. I toss that poncho liner over the whole thing when it really gets cold. I suspect a decent bag could be found for less money and be a better buy.

The only real problem you would have is that it is cotton. The cotton will pick up more dirt, which will get to your down. Cotton also doesn't dry very quick, if you used this for an extended trip it would start to damp and would not dry out nearly as fast as something made for the outdoors. If you were to harvest the down and sew up something in nylon it would be much better, make sure the nylon is down-proof!!

5 lbs. seems to be very heavy.

quote TomT: "....really i see no need to invest in a proper topquilt."

Except for the fact that you would actually have a "proper top quilt".