I 100% agree with you, Neil.
As someone who has run these cars at very high speeds in a road racing environment, I would highly recommend that you move slowly from a high downforce setup to a moderate or low downforce configuration. You don’t ever want to find yourself in the position of not having enough well-balanced DF at these speeds. Be careful about assumptions especially regarding how much front downforce you’re actually generating.
From my experience, I would say that starting in a low DF configuration could be very dangerous at high speed (+160mph). From what I've personally seen with the QRP 25 hour car and with the Raver Motrosports car, the SLC has a tendency to pack air under the nose and front wheel arches causing front end lift in certain conditions. The front end DF or lift would certainly be a concern to me at 200 mph especially with a stock body car without canards, fender vents, flat underbody, side-skirts and race splitter. Keep in mind, that you cannot fully control variables like wind speed, and direction. A gust at the wrong angle at these speeds can go from a pucker moment to a catastrophe in the blink of an eye. Too much rear DF can also be an issue if the distribution of downforce on the car is heavily rear because this can cause the rear to "squat" at high speed, causing more air to be caught under the nose. As the attitude of the car changes, you can go from making decent DF to having significant lift very quickly. I would not underestimate the power of the air moving underneath the car at around 200 mph.
We’ve done a lot on our cars to try and minimize the risk of a Mark Webber/Posrche style backflip. That starts with improving the balance of downforce, specifically by making changes at the front of the car. Since we’re doing a lot of high-speed cornering too, high front end DF is more important than in most applications but it shouldn’t be ignored in this environment either. Controlling the airflow into and out of the wheel wells is really important at these speeds. The potential for the nose to come up and cause the car to take flight is the reason why modern LMP and DPi cars have the top of the front fenders cut away. After that Nissan GTR G3 flew into the crowd at the Nurburgring a couple years ago, anti-wheely strategies were also developed for a number of motorsports control systems what will automatically cut power if the front shocks begin to extend past safe levels. The idea is to cause the weight to transfer back onto the front end driving it downward. We employ this fully automated strategy on the Raver car but I pray we never get the opportunity to test it’s effectiveness.
I’m not saying don’t go run any high speed events. I’m not trying to scare anyone, and I think the car may shine in this environment if properly setup. I would not shakedown a new car in this environment but it sounds like you’re car is past that stage. Like anything else in racing, I would approach it with caution, making small changes to your already vetted and tested setup until you get to a place where you’re happy with the high-speed setup. Once you get that setup dialed in, then you can go for a full throttle, all-in pass with greater confidence in your machine and minimize the associated risks.