I really like ack over grep, and there's a vim plugin too.

https://github.com/mileszs/ack.vim

GNU grep should be able to handle a few hundred small files easily for a few MB of free ram...

That's debatable. For me, typing "gr <expression>" (my abbreviation for recursive grep) is quite fast and convenient.

No, but what about locate, grep and find?

Locate is the fastest, find is the slowest and grep is the most complex but also the most versatile one of these since you can use regexes.

It's the shell and you can use anything you want.

Locate searches the filenames, too.