If you want a nothing-but-bass headphone, why spend $300 on the Beats Pro when you could pick up a Sony XB700 for $80? It too has nothing going for it but bass. I think the entire Beats line is overpriced to shit.
Having listened to both, I think the Ultrasone HFI-580 is an easy step above the Beats Pro, offering head-shaking bass while offering better clarity in the upper frequencies. It is going to be my next headphone purchase for sure. It is also more portable than the Beats, with a lower-profile earcup, and it costs almost ~$150 less.
That being said, if you enjoy the Beats Pros, then buy them and never listen to one of the headphones I listed again, else your headphone interest could become very very expensive

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Also, do some research at
http://www.head-fi.org . It's the biggest source of info for headphones online.