How much information can be gleaned about a gpg key by possessing both plaintext and ciphertext?

[Robert J. Hansen]

> I know some encryption schemes reveal more information about the keys
>  used when an attacker has both the plaintext and the ciphertext.  In
>  general, how much information does GPG reveal in such situations?

Virtually none.

> How much plaintext/ciphertext matched data would an attacker need (An
>  order of magnitude is fine) before being able to reverse enough of
> the key to be meaningful on fairly modern computers?

Enough to make it far, *far* more cost-effective to resort to other
methods to recover your key.  Just buying the hard drives alone would
exhaust the budgets of large corporations.