I re-enabled Write-Back Cache this evening and re-tested... wtf? This is during off-peak hours too...

My numbers dropped to:

Host: vSphere 4
RAID10: Test Size - 100 MB
Sequential Read : 33.67 MB/s
Sequential Write : 77.10 MB/s
Random Read 512kb : 27.78 MB/s
Random Write 512kb : 83.57 MB/s
Random Read 4kb : 3.711 MB/s
Random Write 4kb: 2.669 MB/s

Original w/o Write-back below:

Host: vSphere 4
RAID10: Test Size - 100 MB
Sequential Read : 151.480 MB/s
Sequential Write : 171.616 MB/s
Random Read 512kb : 131.722 MB/s
Random Write 512kb : 162.868 MB/s
Random Read 4kb : 15.041 MB/s
Random Write 4kb: 9.244 MB/s