Based on your spring rates, if you want to increase your cars' ability to rotate, I would increast the rear spring rates.
On my car, I have 5KG front and 7 KG rear, giving an effective spring rates of about 330 at the wheels. Befor that, I had a 6 kg rear setup which gave about 230 at the rear, and changing up to a 7 kg, made a huge difference.
I still need slightly higher spring rates in the rear though, but I'm out of rebound dampening adjustments on my coil overs. Winter I'll send them out to get re-valved to add another 30% rebound.
But yep... increasing the rear spring rate is pretty cheap, and won't bump you up any more than where you are now.
Or if you really want to experiment with rotation, swap them around, put the high rate springs in the rear, and hang on to your hat.
Also tire pressures play a huge difference in the ability to rotate. At the SPDA we run huge differential pressures between the front and the rear.
We'll get to that at another time though.
Hope this helps.