After thinking about it I decided to crunch the numbers just to see how much of a difference the weight of the fabric would make. Going from the numbers I got from making my DIY blackbird hammock, Climashield TQ, Insultex UQ, and Cat Hex Tarp (plus carrying sacs for each) I used around 25 yards of fabric. This came off a 60+" roll so lets just round that to an even 40 square yards of fabric.
Now this number could be off by as much as 5 yards or so but its a close enough estimate to make a comparison. The Taffeta comes in at around 2.6 ounces/sq yard and the eBay ripstop nylon is 1.5 ounces/sq yard. So that brings the nylon total fabric weight to ~60 ounces and the Taffeta to ~105 ounces. For a grand total of 40 ounces between the two choices. That is 2.5 lbs!
Since we're hikers I really think it would be best to go with the ripstop nylon in this case. If only she liked camo this would be a lot easier since I still have a good bit left from my magnafabrics order!