Not easy to say, on average I think its around 10% loss from FW to RW dependent on drivetrain, some calcs say its as much as 17% loss. I never really took notice of rwhp, fwhp is the key as nobody can accurately say how much every particular car will lose.

A true 500fwhp in 3200lbs at the track would be =
60 Foot E.T. : 1.50 ******
1/8 Mile E.T. : 6.82
1/8 Mile Trap Speed : 99.61
1/4 Mile E.T. : 10.81
1/4 Mile Trap Speed : 124

500hp on a dyno won't of course be 500hp on the track as you know so if we say 470 on the day depending on conditions/tune etc. its>
60 Foot E.T. : 1.53 *****
1/8 Mile E.T. : 6.97
1/8 Mile Trap Speed : 97.58
1/4 Mile E.T. : 11.04
1/4 Mile Trap Speed : 121
so your guess is pretty good...however these numbers are from Wallace who base things at 0 altitude I believe?...they were almost spot on for all my calcs on my cars which ran at Santa Pod which is 0.