Hmmm, given that most mods simply up the torque and Kw rather than extend the rpm range (unless one has rebuilt, lightened, blueprinted and balanced the engine), then while I accept that improved breathing certainly helps achieve the high rpm registers more easily, the useable power range of the car remains pretty much in the 3000 - 5500rpm range (and I suppose 6000 would be an acceptable upper change limit under duress). This is probably why some tweaked engines have blown up too. These motors, even stock, turn out a surprising amount of torque from low rpm and keep the curve damn flat until it falls off after around 5000 - 5500. I think many blow-ups are a legacy of repeated high torque loadings from relatively low rpms, eventually leading to a failing rod. Tweaking the engines is simply upping the torque and hence engine loadings, especially if one habitually pulls hard from low rpm in higher gears. On that, while I find the car pulls like no tomorrow from relatively low speeds in almost any gear, I've found that mine is much happier if I keep it spinning faster than has been my usual habit, certainly over 2500 and more realistically around 3000, and I find it tends to handle all the boost air better too, with fewer instances of low engine speed compressor stall.
CP_e Standback & PNP; CP_e 3" SS Downpipe; Corksport FMIC with Top-mount K&N filter & OEM Ram CAI; Turbosmart BOV; Dashhawk; Prosport Boost Guage; JBR solid shift bushes; DBA 4000 Wiper-Slot front rotors; Hawk Ferro-Carbon HPS Street front brake pads (@ 69,000km); Sumitomo HTRZIII's in 225/45 x 18