Putting on my single tank is like not wearing gear. However, I am surprised by what you say about LP85s. They are shorter than AL80s. Are you less than 5ft tall? LP85s are only about 25" long.
Cave class was brutal. 5mm 2 piece wetsuit in Florida summer temps. Two 108s or 104s on my back (44# each without the regs or manifold), an AL80 stage, can light, 2 backup lights, reels, and for my first dive, I had a 16# weight belt! I had over 150# of gear on me for my walk across the sandy beach to the water. I was able to trim that back to about 135 for the other 9 dives!
Good thing this class didn't have scooters!
Things equal out I guess. I probably get FAR less time on an AL80 than you do. MY SAC rate is frightening high, so I need the big tanks. I really need to work on my fitness more.
-P
And while I enjoy the versatility in diving doubles affords, thus I dive them whenever appropriate, not everyone is built for diving doubles with the same ease as diving a single. Double LP85s hang down to the back of my mid thigh and the rig weighs in excess of 110lbs. That's a large load for a non-deep reef/shore dive in cold water, the key being cold water - we try to keep our dive times, even technical dive times, less than 75 minutes - any more than that is not optimal for body temps and offgasing. I can do 60-70 minute dives to varying depths on a single tank here in the PNW. So why go through all the lifting to dive doubles? No one configuration will be optimal at all times in all places for all people.