3 hard drives, a few questions.

[G]

Ok, here is my current hard drive.

Western Digital Caviar SE WD2500JS 250GB 7200 RPM 8MB Cache SATA 3.0Gb/s Hard Drive



Here are the two hard drives I have sitting beside me.

Western Digital Caviar RE WD2500YS 250GB 7200 RPM 16MB Cache SATA 3.0Gb/s Hard Drive

Western Digital Caviar RE2 WD4000YS 400GB 7200 RPM 16MB Cache SATA 3.0Gb/s Hard Drive


I have only 2 HD slots, so obviously I am putting in the 400gb, but my question is do I replace my current drive with the new 250gb one with 16mb cache? I have no clue what the difference in the two will be as far as working, but also I don't know how to transfer the shit from the old drive to the new, without having to reinstall windows or any programs on it. I don't want to go through that. Also, my current drive has been running strong for a year now, but I just don't know if I should bother putting this new one in, or sell it on ebay.



-edit-

looking on Western Digital's website, my current hard drive is only a 300mb/s, where as my new is 3gb/s. Pretty simple choice here really.