Any HDD is the slowest part (Bottleneck) of any Modern PC, so the faster the better.
not really true, common myth tbh.
The difference between the fastest 4 drive raid 0 and a single 16mb cache 7200 will be minimal in most circumstances. If you're doing high def vid work, and not talking the odd encode i mean real work sure faster transfer rate is king.
but other than the 4 drive raid 0 setup booting into windows marginally faster, games won't load noticeable faster, neither will most things. Vista does a fairly good job of keeping common .exe's in memory and so its starting to load a program from memory not from drives.
Check any benchmarks in reviews for hitachi/raptor/7200.11 drives. a single raptor vs raid raptors vs single hitachi and raid hitachi's showed something along the lines of 2-5% game loading time decreases from fastest to slowest responses. Even though a hitachi has what 80-90mb sustained transfer and the raid 0 setup had about 80-90% faster transfer speeds. likewise the raptor with slightly slower speeds but much faster access didn't give any boosts.
Theres lots being done besides loading, obviously, if it was 100% based on loading data then the time taken to load would have dropped a lot with a much faster setup, it didn't, in almost any game or application.
THe difference, tbh, between the fastest and slowest drives available are marginal at best. the slowest drives around now are actually pretty damned fast, and the difference between a 7200.10 with 16mb cache and a 7200.11 with 32mb cache and bigger platters are very small in real world use. sure hdtach/hdtune show prettier numbers and windows loads in 24 instead of 27 seconds, thats about the biggest difference you will see.