It sounds a little funny around 9 -12 seconds into the video. Almost like the car laid down for a second, then upshifted.
I asked John about it and this is what he had to say...
When I shifted to 5th, the power just blew threw the clutch so I shifted to 6th. The clutch packs are definitely a week link at this power level.
Hennessey GTR700 pulls 1 g off the line on its way to a 0-186 mph run in 24.79 sec. The stock R35 GTR takes 53.3 sec. to attain the same speed.