I'm sure someone with a Tornado configuration will chime in. Until then, I believe a 10" length spring is pretty common, but all of the next information needs to take into consideration your specific geometry, angles, lengths etc. I wasn't sure about your query on dropping the wishbones. If I did that, they'd go full vertical because I have no stops, so that isn't a way that I could do this.
I determined my spring values by deciding what amount of travel is expected on my suspension. At ride height, some road cars have 3" +/- travel, which would be 6" total travel for a soft ride, but I would consider that excessive for our cars. I actually bias that toward the droop, and go with 2" bump, 4" droop, but my travel is more in the area of 3" or less.
I determined the sprung weight at each spring, divided by the ride height compression I want. But that has to include, the movement ratio (shock : upright). So for example, I have about 500 lbs on each rear wheel. Divide that by the desired compression of the upright at ride height. Mine has a compression at ride height of about 1.5", so 500/1.5 = 333 lb/in springs. My movement ratio is about .9, so that squared makes the spring rate higher, and now I'm looking at about 410 lb/in. I'm actually running 450 lb/in springs in the back. Coil bind in not an issue with that little amount of travel. If you want a softer, more compliant suspension, then softer springs with more ride-height compression can be used.
In terms of length, you will want to know where your max droop will be, and then ensure the shock is longer than that, and the full bump is hit before the shortest length of the shock. Again, with my 1.5 in compression, it allows a 6" total travel shock.
Front suspension is done the same way, but movement ratio on the front is less than the back (about .70), so even with much less weight on the front, I'm running 350 lb/springs on the front. With all of that said, I've never observed hitting the limits of my travel either on the road, or on the track. The springs do unload when jacking up the car, but that isn't necessarily a bad thing.
Sorry for the vague answer, but unless someone chimes in with direct relevance to your suspension geometry, you'll need to look at what you have (angles, motion ratios, unsprung weights, ride quality/height/compliance desires, and go from there. By the way, even a stiffly sprung car doesn't mean an objectionable ride if good quality shocks, and appropriate settings on those shock are made. You may even decide a different length spring is needed for your application.