Don't listen to black--rider, the twat's talking kak... again !
Quite a few years back I tried a number of so-called running sacks by Deuter, some from Karrimor, and a few own brand from Blacks/Millets.
Each type quickly developed faults such as the stitches giving way, shoulder straps cutting/inverting/tearing and frames breaking.
Luckily, and due to the amount of miles I was putting in, I could take each pack back & try another. (While the shop backloaded the wrecked examples.)*
In the end I settled on an after market military daypack that took the weight.
The one I used was from Extra Range/Rangemaster, but Vanguard is just as good.
Remember that mil daypacks are designed to carry weight & while they might look more expensive than the civvy ones, you do get what you pay for.
* Two points:
1. Take your MOD90 for a discount.
2. NEVER tell them you're carrying a couple of sandbags in the pack !