The LSI 9260-8i has 8 x 6Gb/s SAS ports and that's the amount of throughput you'll get.
However, depending on your workload/application, disks rarely run at 100% throughput. It's more likely you'll reach the max number of IOPS of your disks (unless you're doing bulk reads, streaming, etc).
It also depends on how your SAS backplane "exports" these disks. For instance, some backplanes will have as many mini-SAS or standard SAS ports as there are disks. Others will use an expander like the SuperMicro 846E1 (24 disks for a mini-SAS x4 port).
SuperMicro has a chassis that (TQ edition) that exports all disks individually, in that case you'd need 3 x 8-port HBAs to connect all 24-disks. It makes cable management a bit trickier but has better performance.
My suggestion is that you first determine what workload your application will be throwing at this server before considering it doesn't fit your needs. If it's a NAS/SAN appliance, pay attentio