Could you please post the full contents of the global_prefs.xml and if it exists the global_prefs_override.xml files in your BOINC Data directory?

Could you also tell which projects you're attached to, or at least which you have work from and are running -with which applications?

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Multi-threaded tasks like Milkway's very rarely approach 100%, because there's usually one or more threads waiting to synchronise intermediate data with the others. I'd leave that one out of the hunt for now.

But the others should be OK, and there are no obvious problems with your prefs files. The new Einstein CPU search is very sensitive to CPU cache size - see Gravitational Wave search O1AS20-100 F and I FAQ - your Intel Q8400 might have been placed in the wrong category, and with four tasks running might be starved of cache memory.