The "speed hole" is good for another 1-2 mph! My CM91 has it as well.
The C70 does not. Very slow
If whatever crack you see remains the same and isn't causing any issue then I wouldn't bother with it unless you're going for a show bike, enjoy riding the motorcycle. If it grows then reach out to Honda customer support, replace it, go aftermarket, or get it welded.
Sometimes you have to remind yourself these things aren't going to space, they're just imperfect little motorbikes that take on wear and tear with use. There are countless motorcycles out there racking up miles with chipped and missing cooling fins.
Here's an assortment of functional issues, things to actually worry about, and often worth repairing when parts aren't available or cost an arm and a leg:
1919 Harley-Davidson model J cannonball motorcycle with many chipped off jug fins and replacements welded back on. Cast iron.
1948 Harley-Davidson Panhead,
Sean Jackson's 2023 Biltwell People's Champ motorcycle, undergoing repair to the original cases. Aluminum.
Harley-Davidson JD cannonball motorcycle repair to a cracked jug at the valve pocket. Cast iron.