I'm debating which processor I should get for the MBA and good battery life is one of the main things I'm looking for. I'm a college student and I only intend on using my MBA for word processors, music, internet, photoshop, ipod stuff, etc.
i went with the 2.13ghz, just because it puts my mind at rest, so i don't wish i upgraded later.
i have similar uses to you, and the 1.86ghz is overkill itself, so i wouldn't bother with the 2.13 if i was you, unless you have the spare cash lying around.
you'll only get a few less percent battery life, so don't let that put you off.