Ok, I temp tested the coil, and it helped a lot, though I've still got a slight drive line issue - I'll have to adjust it and see if that helps (the width was way too low, I haven't installed the coil yet premenantly, so I couldn't adjust it).
The HV is now an 'exciting' 19kv at min brightness, and 17 or so at max. There's still blooming slight but you can adjust focus to stay good.
I'll play with it next week - this week I can't get to the set because I've got a field call in Puerto Rico, which is going to last all week.