Ok, my last reply, if you get it good, if you dont too bad.
36GB raptor = ONE 36GB platter
74GB raptor = ONE 74GB platter
150GB raptor = TWO 75GB platters
ASSUMING ALL 16MB cache
the 150GB will be faster at EVERYTHING because it has higher density platter (75GB vs 74 vs 36) but mostly because it has 2 reading heads moving at the same time as opposed to the other drives which have one. The 74GB drive somes very close to it in benchmarks (the 150GB generally performs 10-15% better), and actually beats it sometimes in latency benchmarks (like I told you, it all depends where the files are placed on the platter). The 36GB drive falls far below because it has much lower platter density. Even thou it spins at 10k it only comes across so much data.
Think of it this way, if you have a saw moving at 10k RPM, and you have 100 pieces of wood to cut, which way are you gonna get them done faster, by cutting them one at a time, or 2 at a time? Double density = double the data the heads spin on top of.