The SATA2 Interface is 2X faster than your HDD, oddly the Write speeds will be faster on the Intel SATA and Read about the same. On the bright side most SATA3 HDD have a larger cache so the few bucks gives you something.
Don't feel anything bad, WD does a good job convincing most people SATA 6.0Gb/s suggests speed, it means SATA3 interface. The WD Caviar Black are fine, and the R/W is 140MB/s~150MB/s. SATA2 is a 300 MB/s interface and the SATA3 is a 600 MB/s interface. The Intel is a more mature and stable place for your HDD.
Try both and test both - why not...
People all over are freaking out realizing most SATA3, in particular Marvell 912X, is crapping out ~400±MB/s and NOT the assumed 600 MB/s. Meaning SSDs like OCZ Vertex 3 that are capable of R 550/W 500 MB/s are hitting a wall of 370~410 MB/s.
You learn something new every day - all of us