As Gideon says - it is not a straight forward answer, nor a straight forward question - there are literally more than 50 different variables that goes into sizing, including read/write sizes, random vs sequential read vs write, concurrency of workloads, access protocols, version of ONTAP, etc. Depending on this data, it could be 400MB/sec to 950MB/sec, with 11,000 to 130,000 IOPS or more.
If you are concerned that your existing system is running slow, please open a support case and we will investigate.
If you are looking for a sizing for a workload as part of a potential purchase, you need to work with a solutions engineer from NetApp directly as part of the sales process.