If you like the E3, I think that it is worthwhile for you to audition BOTH the ER4 and the E5. The E5 is quite different from the E3 and ER4 since it has dual drivers and gives you a full size headphone sound inside your head and the bass can be overwhelming, at least at first.
I found that the E3 and ER4 can be more easily compared though I liked the certain aspects of both, the ER4 were better in my opinion sonically. The ergonomics are a different story and this is highly subjective - I like the Shure 'fit'.
If you're going to go to the trouble to audition phones, audition them both and see what you like.
I strongly recommend that you listen to just one phone, and no others, for several days straight - don't switch back and forth. This is the only way to acclimate yourself to the sound of that particular phone and allow you brain to pick out all the phone presents. This is an absolute MUST with the E5. When I first listened to the E5 I thought they sounded horrible. After 2 days straight listening, my brain acclimated to the sound and I could pick out all of the detail without thinking about it any longer and they sounded great. Etys have an immediate WOW effect and take less time to acclimate to but this is a good approach and with 2 weeks audition time, you will have plenty of time to spend with each phone. You can switch back and forth at the end of the audition period once you are acclimated to each phone - it's like riding a bike - once you learn it is not unlearned and you can hop back on anytime.