Ryan -
There is no metric for estimated IOs on an aggr, but you can compute it.
See my reply to IOs on a volume:
http://community.netapp.com/t5/FAS-and-V-Series-Storage-Systems-Discussions/Estimate-IOPs-Capacity/m-p/125924#M7786
Given that disk drive utilization on the aggr may be the key metric to monitor.
(<50% average is the Best Practice)
You may also wish to see my Webinar on Cluster mode performance monitoring available at:
http://www.fastlaneus.com/recordedwebinars
I hope this response has been helpful to you.
At your service,
Eugene E. Kashpureff, Sr.
Independent NetApp Consultant http://www.linkedin.com/in/eugenekashpureff
Senior NetApp Instructor, FastLane US http://www.fastlaneus.com/
(P.S. I appreciate 'kudos' on any helpful posts.)