some useful "adjustments"
homepage says GNR has net drop of 22m & kellogg reckons from "10 feet in elevation drop helps you by 1.8 seconds" that is worth ~ 13s
let's see for most noted runs there : mo ran 59-flat & paula a 65'40
for mo's 59'00, the corrected time with 22m downhill :
actual speed is 21097.5 / ( 59 * 60 ) = 5.96m/s
correction speed of : 9.81 * ( 22 / 21097.5 ) = 0.01023m/s
-> correction factor of 0.01023 / 5.96 = 0.001716 or ratio of 1.001716 -> corrected time of : 59'00 * 1.001716 = 59'06
or 6s correction
for paula's 65'40, the corrected time with 22m downhill :
actual speed is 21097.5 / ( 65'40 * 60 ) = 5.355m/s
correction speed of : 9.81 * ( 22 / 21097.5 ) = 0.01023m/s
-> correction factor of 0.01023 / 5.355 = 0.00191 or ratio of 1.00191 -> corrected time of : 65'40 * 1.00191 = 65'47
or 7s correction