I've seen the exact same problems with bronzing and gloss differential at the Canon booth in last year's Photokina with landscapes especially skies, printed on some semi gloss papers and put me off buying one of those. I think was the IPF8300. Has the problem been resolved with the introduction of IPF8400 or not? As far as I know IPF8400 uses the same inkset as IPF8300 so I can't see how.
well at least from what I can determine through suppliers, the IPf-8400 may use a slightly different ink set than the 8300 did when it was first released. I COULD very easily be WRONG. However as far as I know during the first while that IPF 8300 was available it used PFI-704, PFI-304, etc ink models............the IPF-8400 uses PFI-706 and PFI-306 models. That being said, the 706 and 306 carts are compatible with the IPF8300.
It could very well be that the X06 cartridges are the same as the X04, but with a tweaked ink formulation.