Richiebee,
Respectfully disagree. While I know that Winning Colors and Genuine Risk data points are certainly true, the game has changed a bit since then. If possible, thoroughbreds have gotten even more fragile since then. (statistics point that out).
Running a filly, even an amazon filly against colts, on dirt, at classic distances, takes a lot out of a filly. Please see Rags to Riches last year.
There is one bullet in the gun, I believe. If you think you can win the Kentucky Derby by ambushing an inferior crop of 3 year old colts, do it. Winning the Arkansas Derby has no real value. Nobody remembers who won the Arkansas Derby. I am not sure I would be trying the colts with my filly, but if I did, i would be doing what they are doing. Prep against the fillies, then try and step up and beat the colts ONE TIME.