I think I have to go back to agreeing w you when you said hard to say how long they'll last. I just looked it up, abec 11 does not exist as a standard. So any abec 11 bearing is simply including it as part of the trade name of the product.
Abec 9 is as high as the standard goes. So it's hard to say what the true rating is on the bearings you used.
Take a look at abec 9 and you'll see a lot more reputable companies selling them.
bones,spitfire, Boca,
Though typical short boards use 5 so there's enough friction to have a little control , and the 7 and 9 are usually for longboards.