The compression isn't going to harm the crank, but it can be rough on the top end. I'm running 8.25:1 in my Golden Flash and the all-iron top end gets hotter than two hamsters f*&$ing in a wool sock when pushed. It also suffers from chronic pinging. Next time I get in there I'm going to take it down to stock compression ratio. Don't get me wrong, compression is the easiest thing you can do to make your bike faster. I dig being able to hit the ton on a plunger A10, but if I do it for more than a few seconds, the exhaust clearance closes up and it starts to detonate through the exhaust. Long flames shooting from the muffler sure are cool but I can't say it's good for it. Also, once in the mountains after pushing up a long grade it pinged so bad that it broke the electrode off a spark plug. Took me a while to figure out why it would only run on one cylinder below 3000 rpm. ???
Anyway, if you're going to run an iron head and street gas, I wouldn't recommend going over 7.5:1.