Justify Buying new harddisk

I use disk bench to check and see how fast/slow the hard disk I am using daily in order to determine if getting a faster harddisk can make me work faster. Here's the result:

-- Old Office desktop with Windows XP
Size: 2774401024
Time: 136048 ms
Transfer Rate: 19.448 MB/s

-- New Office desktop with Vista
Size: 4614848512
Time: 164237 ms
Transfer Rate: 26.797 MB/s

-- Lenovo X60T laptop
Size: 1355111798
Time: 132047 ms
Transfer Rate: 9.787 MB/s

-- C Driver in home desktop
Size: 1343384636
Time: 125562 ms
Transfer Rate: 10.203 MB/s

-- X Drive in home desktop
Size: 4697620480
Time: 150641 ms
Transfer Rate: 29.740 MB/s

So I swapped my harddisk, and hopefully I get some performance gain.