Not sure if it has been posted before, but here is a link to a polish site with test shots ranging from ISO 100-25600.
They shot this with the 50L @f8 and it's still soft which makes me believe these jpeg shots might have (some) noise reduction applied?
Anyway, the 60d vs 70d comparison doesn't get my hopes up for a significant performance, the 70d looks about the same as the 60d plus a minor boost in resolution:
* iso800: http://pliki.optyczne.pl/C60D/IMG_3442.JPG vs. http://pliki.optyczne.pl/C70D/przyk1/C70D_f14.JPG
* iso6400: http://pliki.optyczne.pl/C60D/IMG_3464.JPG vs. http://pliki.optyczne.pl/C70D/przyk1/C70D_f17.JPG
As always, this is really not saying anything until a final 70d raw converter is out which usually takes a while because ACR is only released every couple of months.