For what it's worth, I'm an ER-4S fanboy who really likes the MS-1. So, probably you'll like the ER-4S...I think. And yes, you'll get sweet, well-controlled highs, if you get a good seal, and more so still if you have an amp.
...but for outdoor use and biking? I wouldn't use ER-4S's for that. The cable is awfully microphonic even indoors and not moving much.
What I use for outdoor exercise is the ER-6i, which has a lot of family resemblance to the ER-4S sound, is a lot easier to drive from a portable, and most importantly, has a relatively non-microphic cable that can be made even less noisy by looping it over your ears and down your back* in the style of Shure and other similar IEMs. I think it's a very good compromise solution, at least for an Ety-lover.
*[size=xx-small]there is a small trick to this: remove the shirt clip from below the junction of the cables, and reattach it above that junction. Now you can slide it up and use it to hold the cables in place behind your head when they're looped over your ears, the same way the Shure sliding plastic sleeve is used.[/size]