Decrypting two XORed compressed messages? If through a previous attack, cipher misuse or two time pad etc. I receive $c=m_1 \oplus m_2$. Where $m_1$ and $m_2$ are compressed messages, for instance GZIPped English text documents. Can we recover something significant about the messages? 

Obviously if we can guess two prefixes we can verify. Can we do more? Can something practical be done about the end if we fail to decipher the beginning? or even don't have the start of the message. 

Since the messages are compressed I don't know of commom substrings except in the header nor do I know how to validate if a short fragment in the middle is plausible.
Update: a premise in the former answer did not resist the acid test of experiment. This whole answer was thus very wrong.

Thanks to daniel's comment for opening my eyes.