I have not heard the 272, but I can try to describe the bass of the er-4s. "Bass"ically, it is extremely clear, tight and extended. However, it is light in weight or volume. When I say light I don't mean lacking really though. This is a huge area of opinion, but I find the bass is pretty near perfect. While it might sound great with more weight, I don't find it lacking. I did have to get used to this type of bass in general, as it isn't compensated for with volume. Instead, you hear the bass and all of it's accuracy and body, but you don't feel it as much as other phones that boost the bass to compensate for the lack of feel.
As I feel the ety need to be amped for best results, you can always get an amp like the c5 or arrow amp that offer bass boosts. The c5 does a great job adding bass to the er4s. I think it can even be a bit much in some music, but a lot of people will probably love that. I listen to my c5 with no boost with the er4s. I find that if you focus on the bass you might start to think it's thin. However, when I simply listen to music and don't think about the bass I'm actually surprised sometimes when I hear low bass and think "did i put the bass boost on"? It simply fits the mix well and sounds excellent. But again, this is something that most people need to get accustomed to; hearing the bass and not feeling it. Not that you don't feel it at all, but just not nearly as much as a boosted bass phone. If you want accuracy and extension the er-4s is excellent. If you want bass that you feel, or you're expecting speaker-like bass (feel not accuracy), look elsewhere.
I would buy them from etymotic. If you don't like the bass you have 30 days to return them.
I didn't.