Hey, that's me!
The topic of 1000whp has been something we have been discussing for some time. Adding something like Alky injection only allows the engine to make the most of the available air, not create horsepower where additional air is not available.
With the H6 at 3.0L, there are two limiting factors that make 1000whp challenging. First, the longer stroke puts some limits on RPM (as does the VERY heavy variable lift buckets). The second is of course the amount of boost you would need.
As a rough calculation, 3.0Ls at 85% eff at 6500rpm at 40psi yeilds about 70 lbs/min of air. Using something around 10-11hp/lb/min of air gets you about 700hp.
If you jump the boost to 50psi, you are talking about 80lb/min, or a bit over 800hp.
You would then need a turbo that can flow that kind of air at those pressure ratios. A 40 couldn't do it, but a 42R could. You would be at the top of the PR map at 50psi, but still workable. If you then added a 200 shot of NOS, you would be in the right ballpark.
If you really wanted 1000hp with no NOS, you would need something on the order of 60psi at 7000 rpm, which would be very very hard to do on any normal turbo. Even looking at a GT60, there is not enough PR height.
If you could rev to 8000rpm at 45psi, you would be at 90+ lb/min, which might be tweakable to 1000hp.
If you could increase VE at high RPM to 92%, 8000 rpm at only 40psi would be close to 1000hp, and right on the GT42 map.
Just some food for thought. Even with a turbo, displacement makes a big difference.