Hello my friend, good morning. Like you say``it should fly´´ , Just a very few road cars can support 600PP without Aero. Like the Ford GT no Stripe or Ferrari 458 Italia.... For sure the ZR1, but 630PP is above the limit i think. Of course you still can drive a car even with 700PP without Aero downforce, but you can´t use it 100%, at this power, any bump is a rampage.
Anyway, a tune for this will not change a lot i think, did you try it like this ? I will check , if it need just some few settings , i´ll do this, but if it need a tune, it will not be for the moment, i´m still involved with the 425pp /comfort soft quest for the actual shootout.
Have a good day my friend.