Each new Olympus model is just a little better with low light. The E-520 is getting a bit old now, the E-620 replaced it and was considered to be a reasonable improvment. The E-P1 another slight improvement, with some tweaking of the latest E-PL1.

I am sure the next E-6xx or E-3 replacement etc. will again move forward. If you have an investment in Olympus glass, then it may be worthwhile seeing what comes to market later this year.

Cheers

PeterB666