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The normal surge testing is at 5kV, which is believed to be the maximum voltage a home could receive from the electric grid.
That is according to Wirecutter which is not correct. Wirecutter may use 5kV...
The actual recognized testing voltage is 6kV , for 8/20 µs. That’s fast. Fast enough to cause a 120V incandescent light bulb to explode and totally vaporize. Nothing left but the metal screw in base.
Video, Eaton- Surge Protection
Video, Leviton Whole House Surge Protection.
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VPR – Voltage Protection Rating. A rating per the latest revision of ANSI/UL 1449, signifying the “rounded up” average measured limiting voltage of an SPD when the SPD is subjected to the surge produced by a 6kV/3kV 8/20 µs combination waveform generator. VPR is a clamping voltage measurement that is rounded up to one of a standardized table of values. The standard VPR ratings include 330, 400, 500, 600, 700, etc. As a standardized rating system, VPR allows the direct comparison between like SPDs (i.e. same Type and Voltage).
https://www.nemasurge.org/faqs/
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https://www.se.com/us/en/faqs/FA370836/
UL1449, 3rd Edition now requires that all SPD Types be tested to verify that the average transient voltage surge is limited to the voltage protection rating (VPR) assigned to the SPD. The VPR of an SPD is often referred to as it’s "let-through voltage" and is determined during a combination ring wave test conducted at a setting of 6kV/3kV . This VPR rating is required to be clearly visible on any compliant UL1449, 3rd Edition device.
Type 1 and Type 2 rated surge protection devices are additionally tested to UL96A "Lightning Protection Systems" specifications, as they are at or before the electrical service entrance. Type 3 surge protection devices are subjected to an operating duty cycle test with a combination ring wave at a setting of 6kV/3kV . This test represents the typical surge encountered at a distance of 10 meters (30ft) from the main electrical service panel. A Type 3 surge protection device is not intended for direct lightning protection, therefore it is tested beyond the potentially effected area.