The shaft has plenty of tip section (5-1/2″). I would start with 1/2″ increments. That stiffen it up about 1/3 of a flex (3 cpm). Reducing the weight in the head from a standard 6 gram to 2 gram might give you another 2 cpm. that would give you half a flex stiffer playing between an R and S flex (if your playing a Regular flex now).
MPF Pro Series Trim: IR27 Hybrid Heads 0″-41″ 1/2″-40 1/2″ 1″-40″ 1 1/2″-39 1/2″ 2″ – 39″
Here’s a nice link regarding your question: