I mean, I guess I'm not sure where to go with this. You won't put down better than 4s to 60 daily driving any more than you would put down 200mph in the same circumstances, because you'll have a V10 roaring at you the whole time and literally everyone on the street will be sending hateful thoughts your way.
But if 0-60 is most important, I'd look at things like that SRT-10 (which makes it in 3.7s stock) or maybe even soup up a CTS-V, which can hit it in 3.3 with some work. Granted both of those, with modifications, will probably wind up closer to $25k than $20-- but who knows, you might get lucky.
Despite that, I maintain my original position: these are far, far beyond just being "nice" cars, and unless you can get a nice computer system for less than negative $80,000 there is no way to get such a system for even one hundred thousand dollars less than these cars, let alone several hundred thousand.
But if 0-60 is most important, I'd look at things like that SRT-10 (which makes it in 3.7s stock) or maybe even soup up a CTS-V, which can hit it in 3.3 with some work. Granted both of those, with modifications, will probably wind up closer to $25k than $20-- but who knows, you might get lucky.
Despite that, I maintain my original position: these are far, far beyond just being "nice" cars, and unless you can get a nice computer system for less than negative $80,000 there is no way to get such a system for even one hundred thousand dollars less than these cars, let alone several hundred thousand.