Respond to bank counter offer with firm stance?

[David Kimball]

When responding to a counter-offer from a bank, what is the best response?
1) inch up the price by $500 or $1000... or even $1500.
2) respond with the same price firm
3) "Serious" counter offer, i.e. 5-10k more.

If it is acceptable to do so, I think I would like to do option 2, because I honestly did not leave any headroom when I offered my best price.
What can I do to sweeten the terms? Decrease closing time from 45 days to 30 days, or is that kind of silly?