SAS is a wonderful type of drive if you want to run a server. If you want it for home use , forget it. They are generally made to handle large numbers of simultaneous requests, not provide peak performance for one or two transfers, and are quite expensive per gigabyte (in many cases, making velociraptors look like a good deal).
What is the difference between SAS hard drives and standard SATA drives in terms of speed and price.
In terms of throughput you'll be limited by the controller and GbE of the N7700 SAS so the advantage of using SAS drives faster than 7200RPM is really for higher IOPS.
If it's just between SAS and SATA of same class (e.g. 7200RPM nearlines) then what SAS offers over SATA is really just those. In particular TCQ has many performance advantages over NCQ under multi-user usage.
My question is, will I be able to add something or upgrade my N7700 to be compatible with these SAS hard drives?
Swapping the backplane for alone should be suffice to convert SATA version of N7700 to SAS as both uses two Marvell 88SE6340 controllers.