[scytheavatar]

I really don't recommend you to go straight for the RS1, not everyone likes the Grado design or the grado sound. You might want to get the SR225 first, it doesn't lose a lot to the RS1 and certainly beats the RS1 in terms of bang/buck.

And if you love the ER4p I think what you should be looking at is the SA5000, which has a very similar sound signature. If you are looking for something more detailed than the HD600 I suspect that you will not be happy with the RS1, cause it's forgiving by nature and far from what I would call a detailed headphone.

 

[tdogzthmn]

I would try to keep the HD600 and get the RS1. That way you keep all your bases covered.