Bye bye RSA keys?

djm answered before I did and with more authority. But to explain in a bit more detail: authenticating yourself using an RSA key involves signing a message with that key to prove that you own it. RSA signatures normally work by first hashing the plaintext message with some hash function and then applying the RSA algorithm to the result. The hash function can be basically anything reasonable, but it needs to be agreed by both parties. From this you can see that there doesn't need to be any particular link between hash function and key size.

Part of the SSH authentication protocol involves agreeing on mutually-acceptable parameters, such as the key signature algorithm; as a result you may well find different algorithms being used depending on the client/server combination.