I know you said you like the extreme powders but you'll get a lot more speed with ball powders. I use Lever with 70 gr BTs. I've also used a lot of BLC2.
I've used a lot of Xterminator and H335 for the 55s.
Extruded powder will work but it will most likely be little slower.
Load data for the 6arc I think is fairly similar.
