The best "fix" for Windows 8.1 is switching to a supported OS or building your own slim ISO using trusted tools. For 99% of users, the 4GB official download is worth the wait.
This gives you a "fixed" ISO without malware. highly compressed windows 81 64 bit fixed
Use the Task Manager (Ctrl+Shift+Esc) to disable non-essential apps under the "Startup" tab. The best "fix" for Windows 8