Within the 14 days, you can return for any reason. Theoretically, you can return your MacBook Air, and then turn around and buy a new one. That said, I don't think you'll notice much difference with the Samsung. I had a Toshiba on my 2010 and a Samsung on my 2011. The 2011 is a lot faster because of the CPU, but disk-intensive operations are about the same (i.e. it takes about the same time to start an application or copy a large batch of files).
Thanks. That's reassuring about the speed difference. The difference looks a lot on paper but under human senses, maybe not so much? I'll think about it some more...