no.. most ppl dont know how the windows experince index works.
There are certian lock in attributes for each part.
for ex: if you dont have lets say 60gb for HDD space then the max you could get is 3.9 and so on(this isn't scritly correct).
the 150gb is probably rated in gigabytes (1,000,000,000 bytes)
but windows vista by default rates HDDs in gibibytes (1,073,741,824 bytes)
so 150gb = 139.69838619232177734375 GiB
is you partitioned it in half and we say its 139 GiB then each partition would be 69 GiB
8GiB is reserved for the virtual RAM.
now your down to 61 GiB.
AND FINNALY WINDOWS VISTA X64 HAS THE SAME SCALE AS X32 SO 8GiB OF RAM IS 4GiB EVEN THOUGH YOU CAN USE 8GiB AND THE MAX IS 5.9
PS also for RAM latency and speed is also rated.