The inches of fish per gallon rule doesn't work for salt water. You are going to have to go to live aquaria or similar and research each fish you are interested in.
I have the first generation nwb200, which is your octo 8" skimmer, and it's not a bad skimmer. The footprint is somewhat large though, and I can't find any information about how much air it draws. I would prefer an Octo extreme with the Sicce psk1000 pump.
I also have a Bubble Magus cone. While the acrylic is a little thinner than the Octo, it seems to pull more crud for it's size. Both are about the same in terms of noise. The BM's footprint is MUCH smaller though. Mine is the BM180EX with the Atman ph4000, which pulls 1050 liters of air per hour. As for longevity....I'm not sure. I have used this skimmer since Oct of 2011.
I would recommend BM products.