I'm gonna go down the ZH route personally. On comparing SuperPi charts with what each can do, the ZH comes off if you can get the high FSB. The ZH also allow for better timings at higher FSB. It also sports a black spreader compared to a poofy cyan/blue. 
ZH - 9 x 295 1:1, 295 MHz, 2.5-4-4-8 2.6V - 31.97 s
ZX - 9 x 272 1:1, 272 MHz 3-4-4-8 2.8V - 34.80 s
EDIT:
Note: These results came from a reputable site using the same workbench system.
http://www.techpowerup.com/reviews/GSkill/3200-2GBHS/2
http://www.techpowerup.com/reviews/GSkill/4000-2GBHZ/2

ZH - 9 x 295 1:1, 295 MHz, 2.5-4-4-8 2.6V - 31.97 s
ZX - 9 x 272 1:1, 272 MHz 3-4-4-8 2.8V - 34.80 s
EDIT:
Note: These results came from a reputable site using the same workbench system.
http://www.techpowerup.com/reviews/GSkill/3200-2GBHS/2
http://www.techpowerup.com/reviews/GSkill/4000-2GBHZ/2
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