Whats the heaviest spring rate you are or have ran on your 8 shock E Maxx and you are or were happy with?

Going too heavy can give you a bouncy ride, so I don't want that but I'm still searching for that sweet combo. I'm using the springs that came with the TBS adjustable shocks. They feel stiffer than the white Traxxas progressive but I still have to crank down on the ring and run it about 1/2 down the body just to get close to the ride I want.

Also, how many of you guys run different rate spring per corner, meaning do you run a weak spring next to a stiff spring? Not on the same shock to mimic PL Power Stroke but one spring per shock of a different rating. Is it worth it? can you tell the difference? It's seems to me the stiffer spring would negate the softer spring from absorbing the small rough terrain.