Most of what you seem to be weighing are nebulous issues of who says what. Why don't you just find out for yourself?
Ask Netapp for an F760 to try out for 2 weeks.
Ask EMC for an IP4700 *at the equivalent price and disk capacity, with RAID* to try out for 2 weeks.
See which has better performance for your users and which you can administer easier. Build large RAID groups, test simultaneous file sharing from NFS and CIFS, fail drives, do rebuilds, etc.
Bruce