Tighten thresh #1483

Job	Run time
macos-latest: clang++ Release Threads	27m 17s
macos-latest: clang++ Release OneTBB	3m 42s
macos-latest: clang++ Release PaRSEC	3m 27s
ubuntu-20.04: /usr/bin/g++-9 Release Threads	1h 0m 24s
ubuntu-20.04: /usr/bin/g++-9 Release OneTBB	2m 20s
ubuntu-20.04: /usr/bin/g++-9 Release PaRSEC	2m 36s
macos-latest: clang++ Debug Threads	21m 17s
macos-latest: clang++ Debug OneTBB	4m 40s
macos-latest: clang++ Debug PaRSEC	2m 59s
ubuntu-20.04: /usr/bin/g++-9 Debug Threads	45m 9s
ubuntu-20.04: /usr/bin/g++-9 Debug OneTBB	2m 25s
ubuntu-20.04: /usr/bin/g++-9 Debug PaRSEC	2m 35s
	2h 58m 51s

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