I don't think you are going to dislike the sound of the DT1350 but I don't see what you are gaining. It certainly won't be in soundstage with a closed on ear HP. The W4's imaging and space is the most impressive of any of the IEMs I have every tried in my limited IEM experience.
The DT1350 is prolly one of the best options to have on your head for a workout in the sense that the split headband helps hold them very firmly in place on one hand, but on the other it is hard to imagine having pleather cups on my ears while sweating and all that. Plus I personally have to tinker with them to find the sweet spot in terms of proper seal to get get every bit of depth out of them so I could imagine depending on your workout this may or may not be a problem preserving that seal while being active. They do have the bass speed you desire and you get low extension at the same time and they are not really bright like the DT series. More mid less sparkle.
Anyway I think sticking with the W4 on sale right now is a wise choice for workout purposes but the 1350 won't disappoint either in terms of sound.
Edited by Doc-holliday - 11/24/12 at 2:21pm