It's an impressive fabric too. 1.7 Hybrid Robic single layer.
If my fat azz can stand in it... gotta figure it makes a decent pack. I had one of my 350lb+ testers blow a hole in it with a bridge pole and then sleep in it with the hole for 30-40 nights. We patched it with tenacious tape and he's been going for 100+ nights in it.
The Hex70 with PU coating is another option from Kyle too that is a bit stiffer (because of the coating) but not as knarly as the 420d stuff.
As you say... the robic gridstops are tough to find in nice colors unless you buy a full mill run to your own specs.
Keep in mind... most of the cottage backpack guys (other than the xpac folks) are sticking with a 70d or so with 100d reinforcement. Even the beefy ones aren't going much past 210 for LD hiking packs... so the 300d HyperD is still pretty stout stuff relatively speaking.
Mystery Ranch Terraplane is 500d cordura... that's the grandaddy of bomber packs if you want to talk overkill.
Not that you need anymore options
One final thought. If you're worried about snags, one thing I've seen used but haven't tested much is doing a super slick rainfly material and making a double layer pack body. Or doubling up the side panels with that material to increase the slid past at the shoulders as that's where you tend to get snagged up on overgrown trails.
But what a lot of folks miss is all the pocket mesh will get trashed pretty quick if you're bushwhacking. Really the only way to go for true bushwhacking is to go with a bit more volume in the main pack and reduce or eliminate any exterior pockets. But if you're mainly talking abrasion resistance sometimes the simple solution is just a second 'wear layer' in sil-nylon or similar.
The best bushwhack packs are the tube style packs- with a minimal back mesh pocket, nothing on the sides and ideally a front pouch to move up the missing storage at the sides of the pack.