Was just about to update.
The meat when finished was awesome but I wanted the bark to firm up a little so drained off the juices from the foil - in a jug to save as a dipping sauce - and then opened up the foil and put the butt back on at 250f for an hour-ish.
I think if I had left it unfoiled for an extra hour or two it would have achieved this before I foiled it anyway - but I wanted to go to bed
Turned out a good sweet meat with a nice heat from the rub and marinade/dipping juices. Nice smoke ring and good bark (colour was already there but texture only happened after an extra blast on the WSM). Not sure if cooking it slower made much difference although the meat was more uniformly soft and tender when I find at 250f+ certain parts can be over-done by the time the thicker parts are ready. Anyhoo here is what it looked like and was received well by all;

