I have cross processed countless (as in way over a thousand probably many thousands of) rolls of e6 film in c41 chems. I have tested every e6 film I could get my hands on, except Agfa's, and I have NEVER found an e6 film that required or benefitted by 2 stops of over exposure. Most films will require testing to find the best exposure as well as development and filtration.
If you over expose it by 2-stops you will get a neg that stops light. If you over expose it by 2 stops and pull it 2 stops when you process it you'll get something interesting.
If you over expose neg film 2-6 stops and process it in e6 chems you will get an interesting slide.
The APUG Conference will have a crossprocessing WS that will include film testing.