I'm running a Speed Passion Competition V3 6.5R motor on a Hobbywing XERUN 120A V2.1 ESC. 19T pinion and 79T spur.
I believe the red Tamiya springs are the softest ones? I can cut them, and try them on. Maybe that helps.
Anyway, the first things I'll try is adding some weight at the rear, and loosen the rear diff a little. If that doesn't help, I'll try the other springs, change the rear camber and maybe the rear toe angle.
Thanks guys!
\Martin