Which languages today would have the least intelligibility with their ancestors from 1,000 years ago?

Assuming you took a modern day native speaker, sent them back to c. 1024 CE, and had them talk to and listen to someone from the 'same' speech community of that time period, which languages would show the absolute least amount of mutual intelligibility?

Assume also that we're talking only the spoken language - no writing involved, on either side. Also, the modern person should have no prior exposure to the ancient language, e.g. no Beowulf enthusiasts talking to 11th-century Englanders.

And what about the opposite: which languages would show the most mutual intelligibility? And what about ones with extremely asymmetric intelligibility?