headphones

I am looking for a replacement headphones to listen to MP3's on a Sony
-Ericsson p900 mobile phone, and cash funds willing, an iPod in the near
future.

I'm looking for something smallish.
I've had a look at a few:

Sony MDR-EX71SLB earbuds
Sony S2 MDR-G57G Street Style
Sennheiser PX200
Sennheiser MX50

So far the PX200 is tempting me but will my SE P900 be able to power it?
Will the 'bigger' headphones achieve less volume than the smaller one?
Overall I'm looking for max volume and of course best sound quality. I
listen mostly to Jazz Funk and Soul.

Has anyone had any experiance with the above choices? New product idea most
welcome.

Thank you