I'm one of those that was looking for X heads to get a slight flow advantage in an SCCA class that doesn't allow porting. I still don't have a set and its not worth the slight initial advantage over the 2.09 equiped J O U. A good valve job could equalize the difference. So even from performance point of view, with a 360 going with a pair of Js makes more sense. Modifying an unmodified X doesn't really make sense dollarwise or performancewise.
That's my .02
