Which McLaren, the F1, MP-412C or P1?
The P1 is definitely the scariest of all of those, but I think the Hennessey Venom GT has most of them beat. Then again, the Venom is half American and half British - but it still demonstrates that when it comes to creating raw power nobody can outdo the US.
I think the Vision K2 could have been the answer, and the Vector WX-3 certainly blew the socks off McLaren and everyone else for a while with its 3.3-second 0-60 time and 250mph top speed. Of course, this is all based on stats, I can't cite any tests. I do think that the MP-412C is beautifully styled though.
If I had to choose the real US answer, though, I'd say the Saleen S7 Twin Turbo.