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The first screenshot shows the parameters of a web browser using the flash plugin installed in the system with GPU acceleration enabled and a cache directory.
That configuration should give the best performance!
If that flash game also has problems with cefclient then these could be the causes :
An unknown CEF3 bug.
An unknown Flash plugin bug.
An unknown bug in the GlobalCEFApp.SitePerProcess feature. Try setting GlobalCEFApp.SitePerProcess to FALSE.
That game may be included in a web page with ads that are blocked in Chrome but cefclient shows everything. Those ads may be the cause of the high cpu usage.