With the right Distro the Z is fine with SDHC cards, mine in fact runs from a 8GB SDHC Card just fine. Debian's kernel sees the card, Cacko for instance would not, so its based on what kernel and drivers are provided.
But for a fact the physical hardware in the Z which reads the SD card can read cards bigger than 4GB's, the max is unknown as far as I know, but mine runs 8GB so its above that