^Single PCI-E SSD will match the IOPS without the controller overhead.

As a followup:
It's also a pretty risky configuration. RAID 10 provides a single drive fault tolerance per subset. Essentially, with an 18 drive RAID 10, you have 9 sets of 2 drives. Each pair of drives in operating in RAID 1. Then the 9 sets are operating in RAID 0. If two drives in the same set fail, you lose the entire array.

1A/1B = Pair 1
2A/2B = Pair 2
...
9A/9B = Pair 9

If you were to lose 2A and 2B, everything is gone. I would advise people against it unless you have taken the risk into account.