Not all finish in the same amount of time, this is why some use foil because that gets you through the stall in a more predictable manner. I do not think 11 hours for a 17-pounder with no foil sounds all that unusual at around 300*.
Now, personally, I do not like to foil my briskets for bark. This is why I cook more around 275 as this also keeps the bark or brisket from getting charred on some parts. I think higher than that and you are looking at a risk of charring.
A lot of folks cook higher, usually around 350-ish, but they must foil to save that bark and the meat from charring. This combo of high heat and foil makes for a speedy cook.
Keep on trucking, and find what you like, and what tastes best to you!