I think there's a file in /cache that will tell you the install error. If it's debuggerred, that may have been altered by stick mount, etc. You can chase down all the update errors and install the correct files, or do a backup and flash the factory image. Side loading the update may be giving the same system check errors. There's also a no wipe method if you're rooted.
I wonder if the benchmark or video apps used in that testing were fully updated and optimized for kit Kat.
Start up does seem slower, but I'm preferring fewer force closes and better touch screen response. Not perfect yet, but that's unattainable.
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