One more variation to consider:
1 OCUM, 1 WFA, multiple OPMs (1 per hub).
Reasoning - central administration through single OCUM/WFA. OPM queries, especially if there are many objects, can present a lot more traffic so collecting locally at the hub just works better, especially in wide ranging collection points. OCUM is deisnged to rollup many OPMs so you have the central monitoring point with drill down to the individual performance details as may be needed.
I've alos noticed personally that OPM tends to run out of gas faster than does OCUM as the number of Filers/Clusters/Objects being monitored increases, probably because it seems OPM pulls and analyzes a lot of data per object.
Have two geographically dispersed locations in the US and one UK location - going with a local OPM at each site and central OCUM/WFA myself as next step from centralized everything, as OPM is the only current pinch point in our monitoring/administration.
Bob Greenwald