Get something that is adjustable in as many ways as you can afford. Bound/Rebound are a plus. The Spring Rate itself does have some effect on ride quality. The issue comes in if you are slammed you need a higher spring rate or as you said you will bottom out or be bouncing all over the place.

Now in all reality slammed is not the answer, slammed handles bad in a lot of cases. Sure it looks good sometimes but in reality you probably lost handling. The car does not need to be on the ground to handle. You want to match spring rates to your shocks and set a ride height. Testing and tuning is going to be necessary to make the car handle how you want it to.

Omnipower seems to be more of a Japanese Tuner setup so I have no opinion on it. I would personally look into something different but that is just me.

Cliff Notes - There is no "right answer" to suspension tuning.