Both cars will weight around the same.
The power from combustion engine will be also similar - around 600hp.
918 have battery pack on it, which increase power for some time.
First time laimed for it was around 7:14, Nismo GT-R did it in 7:08
We are talking about not a weissach-package 918 but normal one.
I belive in real life on road trip longer than 200km which is about 10 NR lap times GT-R could be faster than 918 even its almost 10 time cheaper.
That pretty good engineering from Nissan.