If you're talking about 35 pounds as a base weight (no food, water, or fuel), you might be pushing yourself into a category of very stout, cushioned, and heavy packs, depending on how much food and water you're taking along! Not sure how all the packs you listed will do for large loads; might check with the manufacturer website to see if they have weight recommendations.

But to answer your original question about bringing actual gear in to fit backpacks, yes I do think it matters. For one, it's almost useless to test a backpack without weight in it; you just can't get a good idea of comfort with an empty pack. Second, I like to test with my gear because the sandbags most places will use will all just end up at the bottom of the pack with filling to stretch out the compartments, placing all the weight at the bottom. That runs counter to how I normally pack my items (medium, heavy, light from the bottom of the pack up). Third, I like to check that the gear I'm taking will actually fit into the bag in a convenient way; for example, I've heard that several of Osprey's packs need some tinkering with packing to get the true volume out of it. Doing that tinkering with your gear lets you see if the way you pack it will be comfortable all day.

That's my preference, anyway. Hope it helps.