So I just wanted to post my thoughts on the 1520, and hopefully others can too in this thread.
The hardware is absolutely gorgeous. The build feels really good, and it's barely heavier than my 920, which is very surprising given the size (more on that below). It's also very skinny, and the camera bulge isn't noticeable at all.
But unfortunately, it was a lot bigger than I was expecting! I was trying to take pictures simultaneously with my 920 and the 1520, and I wasn't able to hold the 1520 and press the camera button with one hand. It's just not usable with one hand at all. Also, I'm not sure what I was expecting, but the 1520 doesn't actually FEEL faster than 920. Switching screens, going to email, coming back, going to text messages, coming back to home, was identical in speed on both. I was trying to tap things at the same time to make sure I could see the speed improvements. Maybe it just goes to show how well optimized windows phone 8 is for dual core devices. That being said, the 1520 was just a hair faster than the 920 opening 3rd party apps. For example the camera app was faster by a couple milliseconds, but it wasn't AS fast as I was expecting. There was still a shot to shot delay that didn't seem any shorter than my 920.
I think this might be a fault with the current implementation of wp8, but I fully expect the snapdragon 800 to show it's might when WP8.1 launches. But until then, I plan on sticking it out with the 920. It runs WP8 at 60fps throughout the OS, and doesn't seem like GDR3 gains much from the new processor.