Thanks for the responses.
If the size isn't much of a problem, and the microphony won't really interfere with more dynamic music, then it will have to be the 595's: especially as most of my listening will be done at home. As it is I will have to invest in an headphone-amp to use these with the new Naim Nait5 amplifier I just ordered: so I suspect that the 595's are going to benefit most from this set-up.
Yes I might look ridiculous with a big set of cans attached to my personal stereo, but assuming the 595's are circumaural, at least my ears will be warm. As pp312 said, they could be AKG's.
With regard to them being open-backed, that's something I'm going to have to live with. I recently auditioned a set of closed back Sennheiser HD25's and I just didn't like the in-ear sound at all.
The only other thing that is now holding me back, is the question of whether or not a portable stereo will be able to power the 595's. I recently read some comments that the HD 600's were near impossible to drive from a personal system, and I was wondering if the 595's would suffer from the same problem.
One last thing. Do the 595's have a straight cable, or is it coiled?