It changes from site to site. I have played on Stars at 25nl, 50nl and 100nl. The standard at Stars is quite high imo, even at these stakes. Yes there are still fish around, but there are a lot of multi tabling regs even at 50nl. I have played at 100nl but not enough to make a valid comment on.
Now at Party, well the standard of play really doesn't vary that much from 25nl upto 100nl, it really is donk citaaaaaay. I have only played a couple of thousand hands at 100nl but at every table I open up there at least 3 players there with stats at 40/10 or worse and that at 6max. So definately a big difference across sites.