EDIT: What do you have for hardware? Not sure what you consider pretty powerful but a system with a single 7870/7950/270/280 should get 100k PPD. You should be able to get a lot more than that if you have something like crossfire 290Xs or whatever.
Are you sure about those numbers?
I get 150000 with 2x r9 270(each do ~60k) + gtx770(~30k).
cpu=2500k, 13.12 amd drivers, 335.23 nVidia drivers.
Am i missing something? What can be done to boost performance beside overclocking?
If that cpu is folding on same machines as the gpus. Start by taking a look at your cpu load. If it is in the 90-100% range. Then definately pause cpu folding. Folding is not like mining. It requires more resources and heavier strain on cpu. I don't own a 270 but im guessing it should do about the same as a 7950, which could do 75-90k depending on drivers and the cpu feeding it.