While a 6-cylinder can be made to produce ridiculous power numbers, the fact is there is no replacement for displacement. The highest horsepower engines in any cars are heavily boosted big cubic inch big blocks. Also, while a 1000hp supra is very do-able, it is by no means simple! Those motors putting down that much power have been gone through from top to bottom, had every component replaced, they have custom ported heads, custom cams, hybrid blowers, built drivetrains to handle the power. etc. Building any car to have 1000hp is no easy task at all!
As for all the examples you are coming up with, yes they are fast cars, or were for their day, but you are comparing boosted V6s to NA V8s. Most people don't need 500hp in the car they are going to drive every day, so a factory boosted V8 isn't very common. However when they do come along, they are sick engines. You mention the new GTR with 480hp, what about the new supercharged vette engine with over 600hp from the factory? How about the ford GT with 500hp and 500lb-ft of torque? Also, comparing against ferarris and lambos isn't fair because they aren't built for the same thing. The gearing is different, the weight is different, the handling is different, and the top speed is way different. Maybe a 10-year old lambo won't walk a GTR from a stand-still, but watch what happens after 150mph. That's where the lambo shines because that is what it was built for, not drag racing. Oh, and also, I don't know where you are getting your sources, but a 1987GN won't stand a chance against a stock 06 vette. The GN is a great car, and was incredible for its time, but a vette-killer today it certainly is not.
All this is beside the point though, because cars with that much power for the most part really aren't usable anymore, especially if they are turbo'd. High horsepower turbo cars generally have to run very large turbos to get enough air moving through the engine to make that much power. Large turbos give you turbo lag. On the street, turbo lag is really annoying. On the street, it is much better to have either a small turbo that will spool quickly so you don't notice any lag, or to have a positive displacement blower, which will produce almost all of its boost from just off idle. That is what makes the SC birds so much fun to drive, even over cars that have a higher power rating. Power is all about how much air you can flow through the engine. Superchargers and turbos both try to increase that amount by pressurizing the top side of the engine, so many times the limiting factor will be the turbo/blower, not the engine. That doesn't mean that the larger engine isn't capable of more though because for the same amount of air going through the blower, the larger engine will be at a lower boost level and a lower rpm. That means it can take more of it before it grenades. It also means the car will be a lot more fun to drive because you won't have to wind out every gear to get into your power-band.
I think you should drive some more cars before you decide you want to turbo an SC. Specifically you should drive some stock 5-speed SCs, and a few mildly modified ones. I bet those cars will scare you. Afterwards, go find someone with a stock turbo supra and go for a ride in that. I promise it won't be anywhere near as responsive or fun on the street. For regular driving, torque is king, and if you want torque, you want a positive displacement blower, not a turbo.
-91 Cougar LS, coming soon, complete overhaul
with a 427" Windsor.
-90 XR7 5-speed black on black w/sunroof, MP2, coated rotors, double intercooler, 15%OD, ported heads, comp stage 1 cam, 85mm TB, 90MM LMAF, 80# injectors, and ported big valve heads
-98 Mark VIII LSC, Procharger P600b, TR3650 swap and 3.73s.
-90 SC Automatic rustbucket winter beater
-97 Tbird Sport 4.6 Nice weather daily driver
-"Your buddy Mike is INSANE!" -ClintD's dad