This depends highly on your workload. The Hybrid drives you speak of generally only have about 8GB of SSD on them - If you're reading and writing the same ~8GB of data over and over again, then you'll see SSD performance. If you're doing large transfers where the data is read just once or twice (like with video / media servers), then you'll have better luck beefing up your platter storage because of frequent cache misses.
SSHDs are great for desktop users (Given 5TB of read requests on my system, 97% is of the same 32GB), but file servers tend to not have the same usage patterns.
If you have a mixed load of large sequential reads/writes and lots of random I/O on top of that, then I suggest you look at ZFS and use proper platter disks and a good SSD.
For reference, I recently set up a 5x4TB RAID array using ZFS, and it can go toe-to-toe with an SSD for sequential I/O (avg. 450MB/s sequential read on a 10GB file). This is further backed by an SSD as both a write/read cache, which in theory could give between 900MB/s and 1GB/s if half the workload is from cache and half is from platters. It is in effect the same thing as a very large SSHD, but you can customize and build it with enterprise-grade hardware, and easily replace individual parts when they fail.
Note: If you're using an SSD as a write cache, you should use two separate SSDs as a mirrored write cache so that you don't lose data when one fails. You can very easily take two 256GB SSDs, use 6GB from each as a mirrored write cache, and then use the remaining 500GB as a large read cache.
