The best thing Gmail has going for it are the shortcuts. They're the best feature for ripping through an email backlog. I hope anybody working on an email client includes shortcuts for everything. Once you get used to them, it's painful touching your mouse.
Marginally faster. There's only so fast you can make email because you still need to comprehend it. And BTW, comprehension + shortcuts is the killer feature of Gmail. Having a nice GUI facilitates comprehension which allows you to act faster. There are many reasons why an individual might prefer mutt, but "Much MUCH faster than gmail" is overstating the case quite a bit.