So if durability is a huge concern, you should think about 1000d cordura as well. Seems crazy, 1000 is twice as big a number as 500! But the difference in weight is 8 oz/yd for 500d versus 10.8 oz/yd for 1000d. A pack uses a yard, plus or minus half. So if it's a small pack you could be talking 2 oz difference in weight, for double the tear strength.
See http://milspecmonkey.com/customize/materials for strength info.
1000d is still probably overkill for you, but I just wanted to point out it's not as heavy as people think, compared to 500d. I make my bikepacking gear out of 1000d because all of my gear uses just a couple of yards, and the strength is worth it for that application.