Not exclusively a sportcar video (and I apologize if it has already been posted, I haven't seen it in the thread), but it features a BMW Z4 GT3 among other cars...
You Tube - Hakone Turnpike
...and because I love the sound of the Z4 GT3 so much, here is a video I can't stop watching, purely because of the audio:
You Tube - BMW Z4 GT3 Pair Testing