Chatter is always suspension basically too hard (as T3 says you can alter that by changing rear ride height and you've found you can do it with the throttle too)...that's what chatter is, the bike is over so far neither the suspension nor the flex in the chassis, wheels or tyres can dampen the vibrations from the road surface.

Church is ultra fast, flat out (apparently) for the fast fast fast 250 boys once you've got the bike turned, Alan Armour ground his exhaust out there, lifted the rear and crashed...think about that, so take a deep breath and do it!
_________________
Please do not PM me technical questions, if you can't find it on the Forum start a thread