Using hashcat on systems for which you are not explicitly authorized to do so ... is a very, very bad idea. What you're describing is certainly unethical, and may even be illegal (but IANAL and this is not legal advice; consult your attorney).
For a single card in a desktop system, a GTX 1080 is a reasonable performance/price point (assuming a higher-end budget). A 1080Ti is faster, but is more expensive.
For a single card in a desktop system, a GTX 1080 is a reasonable performance/price point (assuming a higher-end budget). A 1080Ti is faster, but is more expensive.
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