I just went to borrow back my old cx300 I gave away to my housemate. I tried to compare all the tips that give me a good fit (the sound is not tinny, there's all the bass there should be etc..), altogether 3 pairs (large foams, standard medium tips and medium double flanges), on both IE8 and cx300. cx300 and IE8 have almost identical nozzle so the same tips fit both. Long story short - I don't see much difference between isolation of cx300 and IE8. cx300 might be marginally bettter, but really, the difference is very small. I think it's because cx300 has a round driver housing that protects the back of the tips, where on IE8 there's just a tip on the nozzle and not much behind it. I like the sound of IE8 so I'm keeping them for now, the only option I need to elaborate is SE530. But I'm definitely not buying them unless I have a chance to try them on and hear them. I have already had one disappoitment with tf10 recently (decent sound, dreadfull fit).