Ive been waiting to cut my 6 cyl springs, but Ill prob cut them this winter. They sit about 1 1/2" too high for my taste.
I think getting those 620's off and putting the 6 cyl springs is going to make a huge diff, it did on my car. Also, keep lowering the air pressure in the tires. I know its different tires than you, but at 15psi on my 26x8.5 slicks I can only pull a 1.57 60'. Just dropping to 12 I net a 1.51. I haven't tried any lower cause I'm worried of spinning the tire on the rim. (no screws yet)