I can check the settings in VCarve when I get home but I'm pretty sure I run at 60 in/min. I run a tinyG and have my jerk settings pretty high (probably too high), but I think there's still room to run it faster, if I wanted to. I just usually engrave fairly small details and would rather run it a little slower to get a cleaner engraving. This conversation reminds me that I need to go in there and do some tweaking to get my circles a little cleaner.
As for the tips, I have definitely broken one off. The diamond is super hard but it's a little tiny piece of diamond glued (or something) to the end of a piece of steel. It is pretty robust but I have run my bit too "deep" (it's spring-loaded, so depth is used to set pressure) and also run it across some hold-downs, and eventually it chipped off the diamond part. It's easy enough to get a new tip (another reason I bought the one I did, you can just order new tips off his website), and you're back in business.