HZ wont make 300 at those timings, 3,4,4,x is a possibility, but even then you're pushing things.
Always thought the ZX had "issues" running over ~ 235-240 fsb with any timings, or has this changed in the newer batches?
Ram to get lower/cheaper end Gskill HZ aint bad, have a kit running 265 3,4,3,x not the best of timings, but not bad for the cash.
Otherwise OCZ EB or Mushkin Redline kits based off infineon CE-6/5 seem to hold tight timings at high FSB's ( this is whats in Mav's ram) the ZX has them too, but as mentioned above for some reason doesnt seem to clock quite as well as other modules...