Hi Duritz
The first thing you should do is work out your "Difference between Win % S/R and the Win % S/R that will yield your Min Edge which is normally approx. 10%.
The formula for the above is Your Win%-(2+(2*Min Edge(.10)))/ avg payoff (to compute this avg payoff do the following (2*your avg payoff($3.60)+2.
based on your figures this should equate to 6.09%.

Now to find the minimum number of races computed to a confidence level of 99% do the following.
(your Win % * your Loss %)*(2.575/.0609)^2. the answer would be 376 races to provide you with a 99% confidence level.

Good Luck