I think the noise performance in all ISOs is in par with the best in class. You can judge for yourself, there are image samples from the E-5 posted on some websites. Here are the links:
http://www.dpreview.com/galleries/re...review-samples

http://www.letsgodigital.org/en/27267/olympus-e-5/

http://www.photographyblog.com/previ...=Google+Reader

http://fourthirds-user.com/2010/09/e..._photokina.php

http://www.43rumors.com/new-olympus-e-5-image-samples/