There is a PG challenge coming up.  From the challenge thread.
https://www.primegrid.com/forum_thread.php?id=10650
 
Welcome to Autumnal Equinox Challenge: 7 day GCW (Generalized Cullen/Woodall Search) from September 22 12:44 UTC to September 29 12:44 UTC

Well old PrimeGrid tradition was to celebrate the Winter Solstice with a challenge, so we'll do it a bit early this time around :)

To participate in the challenge:
 

• Wait until the challenge timeframe starts (or set your BOINC Client download schedule accordingly), as tasks issued before the challenge will not count.
• In your PrimeGrid preferences section, select only the Generalized Cullen/Woodall Prime Search LLR (GCW) project.

Important reminders:
 

• Note on GCW tasks: PRST (the program GCW runs on) has eliminated the need for a full doublecheck task on each workunit, but has replaced it with a short verification task. Expect to receive a few tasks about 1% of normal length.
• The typical deadline for some of these WUs is longer than the challenge time-frame, so make sure your computer is able to return the WUs within 7 days. Only tasks issued AFTER the start time and returned BEFORE the finish time will be counted.
• At the Conclusion of the Challenge: We kindly ask users "moving on" to ABORT their tasks instead of DETACHING, RESETTING, or PAUSING. ABORTING tasks allows them to be recycled immediately; thus a much faster "clean up" to the end of a Challenge. DETACHING, RESETTING, and PAUSING tasks causes them to remain in limbo until they EXPIRE. Therefore, we must wait until tasks expire to send them out to be completed. Please consider either completing what's in the queue or ABORTING them. Thanks!

Let's talk about hardware:

Supported platforms for GCW tasks:

• Windows: 32 bit, 64 bit
• Linux: 32 bit, 64 bit
• Mac: 64 bit
• Multi-threading is supported and IS recommended. Click here to set the maximum number of threads.
• Uses fast proof tasks so no double check tasks are needed. Everyone is "first"!

Intel and recent AMD CPUs with FMA3 capabilities (Haswell or better for Intel, Zen-2 or better for AMD) will have a very large advantage running LLR tasks, and CPUs with AVX-512 capabilities (certain recent Intel Skylake-X and Xeon CPUs, AMD Ryzen 7000 and EPYC CPUs) will be the fastest.

Note that PRST is running the latest AVX-512 version of gwnum which takes full advantage of the features of these newer CPUs.

As with all number crunching, excessive heat can potentially cause permanent hardware failure. Please ensure your cooling system is sufficient. Please see this post for more details on how you can "stress test" your CPU.
 

A little testing of some GCW. 4 1/2 to 5 1/2hrs on an Intel I9-7920x 12/24 core/thread w/AVX512. 5 1/4hrs - 6hrs on an i9-7900x 10/20 core thread. It was with HT off running max cores, either 10 or 12. Was running at 3.8ghz,