Thought my ears were burning up ..... and if you drop a 250w HQI bulb on that M98 ballast it will do the same thing.... BURN UP!

The ballast and bulbs must be rated for the same wattage, all sorts of bad things can/will happen. Now if you modifiy the pendant to accept a 250w HQI holder (I *THINK* it will just barely fit, I know a 150 will with a litte effort, I'd have to go dig out a 250 bulb and my pendant fixture to get some measurements), none the less if you can get it in there safely and power it with the appropriate ballast it would work, Though heat would likely become a serious issue with anything over over 150w without some sort of mechanical cooling. The design I used will drilling holes in a pattern covering what became the top of the pendant just allowed heat to escape by convection, but IMP that would not be enough for the heat generated by a 250. Pretty sure that makes sense...