Laptop Hard drive upgrade querys

Im upgrading my laptop, ive added 2Gb Ram and would like to stick a faster Hard-Drive in...
now after research I (at first) thought spindle speed determined the speed of the datarate to the drive, so I aimed at getting a 7200rpm 300Mbps datarate SATA II 2.5" drive but after checking I see that i can get 5400rpm SATA I drives that also have 300Mbps (3Gbps) Datarate... so now Iam confused as Ive just been looking at Desktop WD Raptor drives that are 10,000rpm and they have just 150Mbps datarate...???

can anybody explain al this? why superfast expensive drives have just 150Mbps datarate and cheap 5400rpm SATA I drives can have 300Mbps..?

(I know 150/300 isnt the 'atual' datarate but the 300 shows that it should be twice the speed of 150)

please help...

I want to know do I have to get a 7200rpm drive or not?

I currently have a 60Gb SATA 5400rpm 150Mbps drive
and was thinking of getting a 120Gb SATA 5400rpm 300Mbps drive ( http://www3.toshiba.co.jp/storage/english/spec/hdd/mk1237gsx.htm )
if the spindle speed didnt matter... i see that MK1237GSX has two disc and 4 heads.. maybe thats why its able to do double the datarate
thanks

 

...(cont)
ive just been doing more checking and from what I can gather SATA II means the drive has PMR (Perpendicular Magnetic Recording) which basically means it has two disks (platters) and thats how it gets the double DataRate @ 300Mbps (or 3Gbps) ... so what does the spindle speed do for it all?

I would reckon that a SATA II @ 7200rpm should be faster at datarate than SATAII @ 5400rpm - but both have 300Mbps datarates in specifications but I suppose the ACTUAL speeds when pitted against each other would be better for 7200rpm??