Dense flakes such as Samuel Gawith flakes or Peterson's Irish Flake take forever to smoke. PPP maybe even longer. The slowest burning tobacco in my rotation is 1792 flake. I smoke it in a dedicated pipe, a Stanwell 63 shape. It is a dublin freehand shape and I guess it is a size 5, but these sizes are variable, so I'm not sure. I rarely finish a bowl of 1792 in less than 3 hours. Lots of relights, though.
My pipe for englishes is a diplomat, maybe a size 3, and a bowl of Nightcap lasts 1 to 1,5 hours. It's not like I try to drag my smokes out or anything. It's just the tobaccos I like the most are like this. And they can't be smoked faster, cause it turns them harsh, destroys the tongue and in the long run probably the pipe too.