The closest diving to Tucson is either Roosevelt Lake, north of Phoenix, or Mexico. Roosevelt Lake is cold; from what I hear, colder than the waters off Southern California. The Sea of Cortez varies; when we've been down there, the temps at the bottom were in the 80s. As I mentioned previously, our LDS gets very little demand for cold water equipment, so they didn't even have a 7mm suit in stock.
Next time I go out to try a cold water dive, I plan to make sure the time-table is a bit more relaxed. No, I didn't try it on in the shop, and I really should have (reference back to the comment about never again trusting size charts). We were pressed for time to get my son the places he needed to go that evening, but even then, it's hard to say if a quick zip-up would have been enough to say whether I'd have gone for a larger suit. I might have ended up thinking the tight fit was normal, and still been in the same condition.
Looking at those tips for wet-suit fitting, the one I rented missed on several criteria. The zipper was stretching the material, and it was hindering my inhaling. As far as the mobility, it felt impaired, but again, that may have just been normal for a wetsuit. Something that thick isn't going to move as freely as a lycra rashguard.
The Body Glove (which was the brand the shop rented) size chart said an XL should fit 6' - 6'3", 195 - 215 pounds. I'm 6'2" and 200 pounds, but the chart doesn't address at all how the weight is carried. Muscle is denser than fat, and therefore will produce more weight with less bulk than that middle-aged spread that haunts many of us. Someone who is 6'2" and 200 pounds of lean, toned muscle isn't going to have the same proportions as someone who is 6'2" and 200 pounds of average tone.
I'm not shifting blame; the shop gave me the size I thought I needed, based on the chart. It was my own durned fault for not trying it on, and letting the schedule get too tight to take more time in San Diego to prepare for the dive.
I might see about trying a dive in Roosevelt Lake with one of the shops in Phoenix sometime, before another California trip. A bit shorter drive, at least.