SSD random read/write speed issues

Hello all!

I recently underwent a pretty big hardware swap on my area 51 alx.  I'm now using the following:

Mobo: MSI x99a gaming 7
Processor: i7-5820k
Ram: 32g ddr4 2400mhz corsair vengence
HD: samsung 850 pro 500gb

and I'm having issues with the random R/W speed on the ssd.

The sequentials are fine but my IOPS is SUPER low.  I feel like I have all of the OS optimizations at the appropriate settings, but I can't get my R/W speeds to where the should be.  This is what worries me:

The SSD hard drive caddy from dell (PN 6XD4C) is labeled sata II.  From what I know, if this was the rate limiting piece of hard ware, my sequential speeds should be capped somewhere around 250 mbps.  But some searching on the Tom's Hardware forums suggests that my kind of anomaly is consistent with a sata III SSD being connected to a sata II port.  

My question is this:  Does this hard drive caddy limit my SSD R/W speeds to sata II limits, or does the problem lie elswhere?  Some have suggested outdated AHCI drivers, but this is a brand new board and I feel confident I've updated all appropriate drivers.

Can anyone from dell confirm this SSD caddy is capable of sata III speeds or do I need to find an alternative solution?