ZFS raid write performance?

[Quartz]

What's sequential write performance like these days for ZFS raidzX? 
Someone suggested to me that I set up a single not-raid disk to act as a 
fast 'landing pad' for receiving files, then move them to the pool later 
in the background. Is that actually necessary? (Assume generic sata 
drives, 250mb-4gb sized files, and transfers are across a LAN using 
single unbonded GigE).