i dont downshift that much as i dont like putting the additional stresses though the engine, transmission and drive train; then again i don't use the boxster as a track car with the joy of having the capability to perform rebuilds.
as i'm 6'3 i'm not big fan of heel and toeing either as invariably there are few cars that i can move my legs and feet about quickly in.
personally, i find with the boxster it seems to pace quicker keeping the car in the lower to mid power band and using the available torque by keeping a good line into the curve finding the correct roadspeed and to power though the bend
if i find i'm downshifting lower than third its probably because either i've ballsed up the entry or i'm driving outside the conditions of the road and it wont be a comfy well paced run but harsh, jerky and likely to wear the shoulders of the tyres down quickly
what i try and do is to take the principles of energy management from aviation into fast paced driving, here is a short clib of the great Bob Hoover demonstrating engergy management (dead stick)
Stopped engine aerobatics - YouTube