Using RSA directly as a block transform is extremely dangerous; the thing you have to remember about RSA is that, more than most other crypto operations, RSA is just a simple math problem. You are vanishingly unlikely to use RSA directly in your code without introducing a vulnerability.
That said, two responses:
(1) Yes, MD5+RSA is slower (and thus better) than just MD5.
(2) But we're quibbling, because bcrypt is tunably slower, designed specifically for this problem, free, and available for most dev environments.
Comments
Using RSA directly as a block transform is extremely dangerous; the thing you have to remember about RSA is that, more than most other crypto operations, RSA is just a simple math problem. You are vanishingly unlikely to use RSA directly in your code without introducing a vulnerability.
That said, two responses:
(1) Yes, MD5+RSA is slower (and thus better) than just MD5.
(2) But we're quibbling, because bcrypt is tunably slower, designed specifically for this problem, free, and available for most dev environments.
Source of confusion: bcrypt is also the name for a utility using Blowfish. bcrypt-ruby looks pretty cool.