The difference between machines with AES-NI and without is night and day; I'd basically consider filevault FDE mandatory on any machine with AES-NI unless it's physically secured all the time and really needs disk speed to the exclusion of all else.
The other great thing is filevault and timemachine now interoperate fairly well.
Yes. Anything i7 or i5 that Apple has used has aes-ni in it. The last machines to fail this were the old mbp13 (2010), 2010 Mac mini, and 2010 MBA. Everything currently sold has aes-ni.
On the new MBA 13 1.8ghz, I don't even notice the hit.
The other great thing is filevault and timemachine now interoperate fairly well.