Well, I would suggest dropping the bar in 2.5 mm increments over time (weeks or months) by purchasing a set of spacer and replacing the 5 mm or 10 mm with new ones for finer control. Flipping the stem and removing largers spacers may be too much. However, 6m of drop is not much for racing, IMO. Take a look at Cleave's or ShovelHD's bikes. However, they have been at this longer and may be more flexible than you are.