Oly's reputation for high-ISO noise is quite overstated. As long as the picture is well-exposed, noise is really a non-issue (conversely, underexposure is a real killer here).
Also, Oly does very little in-cam noise reduction, if any at all. In any case, I find that NeatImage cleans the picture up very well; there are some noise profiles uploaded for E-1/300/500. I use those, it's pretty good.
A lot of times, we tend to zoom in and pixel-peep; this makes the noise look worse than it is. Prints are most of the time a lot cleaner.