What kind of cooker?
My last 5-6 pounder was 10 hours at 225 with half hour in there at 250. Grate temp was running about 10-15 degrees over the grill temp. Ended up with almost 4 hours of rest just because of eating time. Would have preferred 2 hours, but it seems to not have mattered much.
Also, if you watch mad scientist bbq on youtube. He did an A5 brisket. Was good but it wasn't anywhere near as good as he expected it to be and he had nearly 1k in the thing.