As Jeff said, Netapp's RAID-4 implementation is not performance limiting in most cases. Most of the time a filer with RAID-4 will provide better performance than an equivalent product without RAID or with RAID-0. So I'm sure you will be quite pleased in your tests, particularly against a (*snicker*) Auspex. (Be sure to compare the price and number of filesystems in each system configuration as well.)
I seem to recall some public talk waay back when about Netapp possibly offering RAID-0 since basically all you have to do is remove the parity drive. You could simulate this yourself by manually failing the parity drive and letting the filer operate in degraded mode with just the data disks. However, I'm not sure that the code is actually optimized for this case, so there might be some other normal RAID-4 checks that get in the way of realizing any performance gains.
Bruce