Nested ESXi using SSD LUN

I have Workstation 9.something and I have 2 esxi guests and a few 2008 R2 and 2012 servers.

When I put the Windows based guests on the SSD LUN's, they get close to native speeds ~450 - 475MB/s.

But when the esxi guests have a nested Windows guest within it, and I put that nested Windows guest on the SSD lun, it get only ~120MB/s.

The tool I am using is SQLIO for iops and MB/s and set for random read & writes.

Is this normal? Is there a bottleneck to the esxi's disk driver?

I would think I could get at least 400MB/s, but only 120MB/s?

Thanks