No, the speed per Nvidia GPU is real, as I wrote, this speed-up it is not "skip-hash". The speed GPUs run at, such as 6800 Mkey/s per RTX 4090 at full 100% power limit, is not achieved by skipping anything. It is a real hash reached by heavy CUDA optimizations I did. Full keys are being checked at this speed. My version can go even normal one-by-one scanhash with 1 stride at this speed just as original Bitcrack did without skipping anything.
Yeah, this cherry-picking from a cake approach is still based on luck
Are you sure the cherries you're picking are not actually something around 99.999...% of the entire cake? And the remaining 0.000....1% are the excluded patterns? Because this is what some quick and dirty 9th grade combinational probability would indicate.
You are never seeing your so-called "letter and number" strings (basically hex representation of bytes) not because they can never happen, as you wrongly suggest, but because there are massively much more strings that are apparently scrambled (when using the same high-level representation alphabet). In reality, all keys have the exact same probability, no matter how they look like. Excluding keys based on a pattern would mean that randomness also has a pattern (the pattern of excluding your pattern, or a bias), which is a logical contradiction, because by definition randomness does not have any patterns or biases. So by induction, the initial hypothesis "some strings can't appear or are very unlikely to appear" is wrong, so why do it?