Whoa, 800+ for single digits?
Didn't mean to raise the blood pressure.
There are obviously a number of variables, and by 800 I mean flywheel hp which is around 700 rwhp. Also I guessed at the weight (you said a full-weight-hatch), lowering that can make a huge difference (a 2500lb car can get into the 10's with 400rwhp). 1/4 Mile ET Calculator
(this calculator gives a guess without considering many of those variables, it just determines how much horsepower it takes to get a hunk of weight moving and assumes some parasitic losses)
Here's another one, gives similar numbers: http://www.wallaceracing.com/et-hp-mph.php
(use RWHP here).
But yes, guessing at the weight of your car (3300) the horsepower required to lower your ET by an entire second seems to be around 100hp. A 200hp car could do around 15, 300hp in the 13's, 400hp in the 12's, 500hp in the 11's, 600hp in the mid-10's, 800 in the high-9's.
These look like pretty reasonable numbers to me. They also point out the benefits of weight-loss over power-gains.
There are diminishing returns to power (drag, other parasitic losses) once you get to a certain point. To hit the 8's you'd need something like 1200hp. Don't even ask what it takes to run in the 7's.