I think this link might help you calculate the IOPS for different type of disks. You haven't provided the type of disk (SATA, SAS, FC...) and so I cannot calculate the IOPS for you.
You can typically use the SAS figures for FC disks.
Every workload generates different usage patterns, which will be different IOPS figures. IOPS isn't a defined 'thing', so 1000 IOPS for one workload isn't the same as 1000 IOPS for a different workload. Is this all read, all write, some mix? The results will vary a lot.
The reason there isn't a simple figure that you can easily look up, is that there isn't a simple answer.
I work with a rule of thumb of about 2500 IOPS per SAS shelf of 24 disks, and about 1500 for a SATA shelf. A DS14 would be about half of this figure, as it has about half the usable disk count (depending on spares).
Is this a figure you would use as a starting guide to estimate a shelf count for a system? probably.
Is this a figure you would give to a customer as a guarantee and base your designs on it? I wouldn't.
Also keep in mind the huge effect of Flash Cache, Flash Pool and NVRAM in a NetApp. Disk IOPS aren't as important as many people think.