To start, I would find out what the sport spring rates and the off-the-shelf ground control spring rates are.
Lets pretend the Sportlines are 350F 230R (I have no idea really). You can't just buy ground controls with the same rates and expect it to ride the same. The reason for this is that the Sportline springs are progressive, and the ground control springs are linear... and a 400lb progressive spring is going to ride softer than a 400lb linear spring always.
So, common sense would say to get ground controls with a rate that equals the inital rate of the Sportlines...but the manufacturer isn't going to give you the info you'll need to figure that out.
The point here, is if you're just comparing numbers, you want to get ground controls with a slightly softer rate than the Sportlines. Not too soft though, because then you risk bottoming out. Technically you want to go softer based on a percentage(there's a way to come up with a conversion factor, but again, need manufacturer info.) Off the top of my head, I would say go about 50lbs softer front and rear if going from Sportlines to ground controls.
Ground controls offer adjustability that the Sportlines do not, so they are a better setup. One thing I would suggest though is helper springs.
On a "full coilover" setup, the bottom mount rotates to change ride height without affecting preload. With a Koni Yellow/GC setup, you don't have that luxury. So, when the suspension goes into any droop at all, the spring can become loose. Here's a picture for reference. You can see the helper springs on the bottom.
Other than that, you would have to do a lot of measuring and get the car on scales if you want to target a specific ride frequency...but I'm guessing you aren't that serious.
