Is Sennheiser 600/650 an overkill ?

My advise is the Sennheiser HD-497, it should be a good match for your computer. The HD-600 & HD-650 would be an excellent match for an amp that can drive them (300 omhs),
the HD-497 impendance is just 32 ohm and it comes with the
1/8 connector. I am pretty sure that your computer headphone amp won't be able to drive any headphone with an impendance above 50 ohms. In my opinnion the HD-497 would be your best choise for use at work. They are open air design so you will be able to hear if someone calls you.
The in ear type headphones are very good at isolating you from the rest of the world, they may not be a good idea at work. Hope this helps, Hector.

Hepl makes sense. However, if money is not object then look at the headphone amps for sale and combine one with a Senn 600 or 650 for ultimate resolution.

If you want ultimate resolution you wouldn't be listening to MP3s. I'd go with Hepl's advice. The 600 / amp combo will just reveal flaws in the source. There are also good models from Grado, Beyer, etc.

You might also consider a closed back (sealed) headphone, to close out background noise, and so that your music is not audible to others. I use the Sennheiser HD-280 pros, and I really like them. A step up from these is the Beyer DT-831 (I think that's the model).

Thanks everyone!

The headphone will be used in my cube at work with computers/MP3 ONLY, so an Amplifier is not an option unfortunately.

Seandtaylor99: -- I didn't know 600/650's open design will make the sound audible to others! That is definitely not suitable for cubicals. I don't see many Sennheiser Pro or Beyer headphones here on Audiogon though. Are they good with computers?

Abe