I can't see any of the pictures but maybe its just my computer. I wouldn't worry too much about your internal temp because very soon (usually around 150 or so) you will be hitting the dreaded stall and you will be say man this thing has been stuck here forever. haha I normally smoke mine at 225-250 but it will be great at that temp as well. Are you going to foil it at all during the smoke?
How big are the butts? Weight, fat content and thickness can all change the length of time the meat will take to cook. I have had two butts that were very close in size etc. cooking side by side and one will be done way sooner than the other one. You just never know. The saying goes it's done when the internal temp says so. You can't go by time. Good luck. Make sure to post some Qview.