The 1.5 hrs/lb is just a basic guideline, and is for lower temps than the 240-250* range you speak of. 225* is the typical shamber temp used by most, giving a good compromise between a truer low & slow cooking and getting surface and internal meat temps through the danger zone, in most cases. If bulkier cuts of meats are being smoked after using prep methods which rendered them as non-intact whole muscle meats, then, a higher chamber temp may be in order to get internal temps above 140* in 4 hours. Otherwise, 225* will give the best overall results for natural tenderization of the meat, especially when cooking to higher finished temps.
Smoke chamber temps and the resulting grate-level temps will change dramtically with vertical smokers when meats are loaded on the grates. I've noticed this with every vertical smoker I've used: My original GOSM gasser, and with a charcoal conversion, my Smoke Vault 24 gasser, and my Brinkamnn Gourmet charcoal. If you have only one garte level in use, it makes things a bit simpler to control temps, but when you begin adding meat to multiple grate levels, the meat on lower grates can deflect heat out and around the meat on the next grate above it, which in turn increases cooking time, but can also create a high temp flow on the edges of the meat as well, which translates to un-even cooking. If a baffle or water pan is not in place above the fire, then the meat on the lowest grate level will catch most of the heat, while anything above it gets the baffled heat which travels upwards towards the side of the smoke chamber. If a baffle or water pan is in place over the fire, then, the baffle effect is already taking place before the heat reaches the first cooking grate. It's a balancing act of sorts which requires the proper spacing between the baffle and lowest cooking grate and spacing between the additional cooking grates in succession above the lowest grate. Depending on the over height of the smoke chamber from baffle to top, I find my most evenly dispersed heat using a single cooking grate to be at the center of the chamber. But there again, as soon as I load more grates, the flows will change and result in grate temp variations. I have an arsenal of 10 oven grate thems and 6 long-stem analog therms which I've used in the past to make this discovery.
I'm not a UDS user, but the principles are the same. With a UDS, you're dealing with highly reduced flows through the smoke chamber for the purpose of fire/temp control and the resulting increased fuel efficiency. This also can cause changes in the convection process of cooking. With higher flows, lower chamber temps are needed to achieve the same resulting cooking times, as faster moving air will transfer more thermal energy to the food than slower nearly stagnent air. My theory on the darker coloring of the crust shown in your pictures is that with the higher chamber temps, the sugars (if any) in your dry rub have carmelized earlier than might be noticed in my gourmet charcoal or any of my gassers due to higher flows in the smoke chamber.
The dark coloring of the bark has alot to do with the charcoal fired smoker in general. My gassers don't give a very dark colored bark unless I run higher than normal chamber temps, or use higher than normal amounts of sugar-containing ingredients in my dry rubs. While I don't yet know the exact scientific process behind the charcoal vs gas, I do know I can achieve a much deeper and usually darker smoke ring with charcoal than with gas.
Hope I didn't confuse you here...just a small part of what I've learned about the craft of smoking.
A second look at the pictures tells me that you've porbably gotten some sugar carmelization along with some rendered fat charring with the rub...I would be inclined to say that your chamber temps are far too high for brisket and butts. I'd be finding a way to get accurate measurement and take it from there.
Don't fret, 'cause learning how every new rig likes to run is the key. Once you find out what keeps your smoker happy, you meat will look better as well. And don't forget, high sugar rubs on long smokes will carmelize and eventually burn. On ribs, CRS and other smaller cuts, sugars are fine, but for the long smokes, beware.
Eric