Thanks a lot for your advices,
the problem is that I live in central Europe so I can´t reach costco unfortunately
the 550 model costs 530 USD here in Czech Republic, 564 PET version costs 583 dollars and 770 version costs 663 dollars, so there is not so much to think about buying PET version instead of 550 version for me, but the 80 dollars difference, between 564 and 770 version is still on my mind...
Anyway none of you recommended me the 770 version, so u guys think that 564 version will be good enough for me? Some people write on our country´s forums, that the 5xx battery won´t work for more than two years, so I´m kind of worried and this improvement looks good for me. Also if the 770 model has improved cleaning mastery and CHM, than it might be good... but is it really so better that it´s worth 80 bucks?
Thanks a lot for helping me anyway. I really appreciate that.