I recently just installed a new ASM G1X (rated for a 150 gal) in my 75 to replace an older air stone model. From what I have learned from this forum and others is that ASM tends to over estimate the skimmers by quite a margin.
The more experienced people on this forum told me that for a 75 gallon reef, the ASM G1X would be probably OK on the lower end (obviously too many factors for a definitive answer). However, after the "break in" period I do think the skimmer is far superior to the air stone. Much easier cleaning and adjustments. You may want to consider a larger ASM if you have the room also if you do go ASM get one that is rated at least double of what your tank is and you should be OK.
As for Octopus extremes, I just purchased and installed the Octopus extreme 300 for my new 180 tank (it barely fits within the skimmer chamber of my sump). Its huge but very impressive to look at. I will provide updates after I get it running and broken in. Many in this forum speak well of the Octo skimmer line up so I will be updating.
