I agree with you 100% on the crop cameras being used on higher end work. Though the images may look fine, but like you said, it may be noticeably different when enlarged to far.
Like you, I try not to push my ISO too high unless I am going for that grainy look. I think the highest I have ever taken a shot for someone was @ 2500. It looked okay, but not something I was super proud of, but the client loved it, go figure. As long as they are happy, I’m happy.
I swear I am like a special needs kid when it comes to using cameras other then my own. It’s like the buttons and controls are all foreign to me. I was using a friends Nikon D800 and the menus and buttons might as well have been in Chinese. I figured it out but man, did it take a while.
I have a T3i and a 7D as a back up, I would probably never use the T3i for a wedding or similar event, unless I threw a nice lens on the front of it. I rarely ever use it, but it’s there just in case. The 7D, even though it has the same sensor, is much faster and looks to be more sharp, in my opinion. I would go with this before the T3i.
It’s true, gear can make or break a photographer. I had a lucky set or circumstances which I was able to buy my main camera, otherwise, I would have never bought it, too much $$. Since I had the chance, I took it and well, do not regret doing it, so far. I could have probably got 2 5DMKIII’s for the price but too late now, I guess. In hindsight, I hope that by getting that camera, it has allowed me to explore areas of photography that I am not 100% comfortable with. I like taking chances and working outside the norm and trying new things, diversifying in a way.