variac size and flashover

     2 questions for the gurus:
     1)  How big a variac do i need? 5 amps?  15 amps? I'm going to be 
     running a 12kv 60ma NST.
     2) What's the recommended distance between the first turn of the 
     primary and the secondary to prevent flashover?  I was thinking 2", 
     (for a 6" secondary) but now i'm wondering if that's too much. . .
     paul mathus