Right metric for vROps storage performance

I'm looking for the right vROps metric to use for storage performance on a virtual machine.  What I need is the metric that gets me as close to the OS as possible when measuring command latency.  there are virtual machine metrics for "storage" "disk" "virtual disk" and "datastore".  Ideally, I'd like a metric that utilizes VMware tools to measure command latency from the time the OS sends the command to the SCSI controller until the time the OS receives it back.  Is there such a metric that measures storage latency from that high up in the OS?  If not what is the metric that gets up the farthest and closest to the OS?  disk, storage, virtual disk, datastore, or one particular metric within these categories?

Thanks!