Hmm, anyway if there are no differences between pool-speed finally (after 2-4 weeks 24-7 mining for example), why do I not earn about that, what Bitcoin-Calculator says? There are about 30% difference.
It's probably just variance. As other posters mentioned, smaller pools have an increased payout variance - you're putting more eggs (shares) into one basket (round).
A faster pool means shares are spread across more rounds, so 'luck' plays a smaller part. A slower pool means shares are concentrated into fewer rounds. So if you have good luck for a few rounds, you have a great payout. Bad luck means a poor payout. Since the smaller pools have a lower hashrate, a run of long rounds could mean poor payouts for weeks.
Or you could use a mining proxy and spread your shares around as many pools as you can, which (if you ignore variance caused by the payout method) will reduce your payout 'luck' (good or bad) by a much greater degree.