Just tried ver. 42
hovered around 653kp/s
Still slower than the reported speed from ver.40 (reported between 699kp/s and 645kp/s averaged about 670kp/s) for me but a lot closer.
Do you know if ver. 40 might have just been reporting the speed wrong?

Also when the reported speed from ver. 40 was above about 600kp/s it would only report 645 or 699kp/s and nothing else. Was it rounding to these numbers?
Maybe ver. 42 is just a lot more accurate in reporting the speed. That would be good.
Thanks for the quick response and the hard work on proth_sieve!