a) Depends on OC level.
b) Near Sakkara, in the sun? No. But then again if you would leave it in the sun the battery would probably pop anyway.

Each device is different, each takes OC differently. There is no inherent "safe". Some will do OK, some will not. The more heat around, the less your chances of coming out OK in a year or two.

Use your own judgment, because it's your pocket if it goes. IMO, stay lower than others, they may have as much as 25 degrees lower ambient than you. Try to keep voltage lower, as it will give you a better shot at it.

Me, I have some small scripts that pop the speed up and down and if something hangs or cranks the CPU for a while, I immediately ctrl+shift+x and lower it to compensate for heat. If you're outside in 40+ degrees, stick to lower frequencies. The reason I don't use Queen whatshername or desktop shortcuts is that UI is sluggish exactly when you need to throttle down. So, terminal for me.