Recalling the HD555 at £40-50 and HD595 at £60-70 (both excellent value) a few years ago, I've always regarded the HD558 and HD598 as overpriced, although I've only ever demoed them in a shop.
The HD600 (which I own) is frankly in a different league but its more neutral soundstage isn't the most suitable for pairing with some soundcards as a gaming headphone.
I found it suited Xonars with Dolby Headphone very well for gaming. For X-Fi's CMSS-3D Headphone or unprocessed stereo, headphones with angled drivers make them more suitable for gaming than headphones with 'flat' drivers like the HD600. I find it helps with giving a frontal sound presentation, linking the audio with the screen. Dolby Headphone kind of lends this kind of presentation to headphones with flat drivers but I find it messes with the soundstage in headphones with angled drivers.
I've never owned a Soundblaster Z so I'm uncertain on what headphones might be best paired with it.
Are the HD429's drivers angled like the HD598?