Hi RJ,
Max CPU can spike to 99 or 100% utilization in normal usage occasionally, but if it happens often, it is probably indicative of a problem.
Average CPU for the 4500 series switches ranges from 20-40% or higher even when completely idle. Depending on the features enabled and type and amount of traffic going through the switch, your average range could be anywhere.
Here's a good doc on understanding CPU utilization on the 4500 series switches:
http://www.cisco.com/en/US/products/hw/switches/ps663/products_tech_note09186a00804cef15.shtml
HTH,
Bobby
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