When I took my previous Focus (zetec) to the track, I found that the ideal shift point was between 5300 and 5500. The power plateaus or drops off after that, and you're better off shifting to the next gear. Hope this helps.
05 D20 ZX3:
F2 CAI, Trubendz 2.5 exhaust, Tom's Tune, Eibach Sportlines, black SVT wheels