xoc is not defined by a temperature range, it is defined by the type of cooling used and the type of overclocking, whether it is LN2, Lhe, DICE, a chiller, phase change...etc
You can xoc at high temp if you really want (via voltmods to extend overclocking ranges) but that nets lower scores because silicon doesn't clock as high at high temp
Condensation happens below ambient temperature while depending on humidity too
When the temperature of an object falls below the temperature of the water vapour in the air, the water will condense onto the object, that is all that happens
So if you happen to have your graphics card somehow become colder than the surrounding air, condensation starts to occur on it