Hahaha well at times it seems that you can never have too much pancake, that is until you start pouring on the syrup and realize what you were missing! Thanks again for the kind words as I really do try to give my honest opinion to help out, I'm just glad it is appreciated. For comfort I really found both of them quite comfortable. The SM3 was much more comfortable than my Etys, which tended to expand my ear canals a bit and I'd have to take them out to give my ears a breather. It was almost akin to wearing shoes that were just a skosh to small. I didn't have this problem with the SM3s but my ears still needed a break from time to time as it still felt like I was shoving something in my ear. For the customs I really think it depends on how accurately they were made and this relates to the customs themselves and the impressions. I went on a six hour ride with these in the whole time with no discomfort at all. Aside from that I have them in quite often while at work and don't experience any discomfort. It definitely is a different feeling having them in as apposed to universals as they go quite deep into your ear canal but after a few days you get used to the "newness." I assume it's like those "toe" shoes that are all the rage. Everyone says that after getting used to them it's the most comfortable thing on the market lol, but I have yet to try this as I'm not sure I'll ever get used to their noxious odor after a couple sweaty runs.
The isolation is much like Average_joe's comments with the silicone ones at the head of the pack and the acrylic somewhere in the middle and he might be a bit more useful here as he's tried quite a number of these. I used to own a landscaping company and would use my Etys all the time for isolation as they offered more isolation than the store bought earplugs and could play music to boot. The Aud- 5X don't offer nearly as much isolation as those but it is a nice reprieve from hearing nothing but your music to hearing your music and the person yelling at you to move out of their way so they can get off the metro. If you take the Underground (I'm not sure where in UK you are) you'll be able to hear the "mind the gap" but just barely, by comparison you wouldn't even hear the car coming to a stop on the rails. With music playing though, (on the Aud-5X) you'd just barely hear the car screeching to a stop and not the notices over the intercom. As an aside to this, I also noticed that I needed about a quarter of the volume than I did before as the space between the end of the monitor and my eardrum is much smaller. With the Etys I pushed the volume on my iPhone, for example, about halfway to a little over. With the Aud-5X anything over halfway is more than I can handle.