Serial ATA is beginning to make its impact on computers; SATA drives are quickly taking over from the traditional Parallel ATA drives. A quite important fact is that SATA and SATA II are trying to bring business-class hard drive performance to non-SCSI machines.
As we went though the tests, we noticed that our SATA II HDD was slightly faster than the SATA 1.0 HDD. In the HDTach test, the WD2500JS SATA II reported 196.7 MB/s in burst speed, while the WD3000JD SATA reported 121.6 MB/s. In the SiSoftware Sandra tests, there weren't any significant differences, with the exception of the combined index where the WD2500JS reported higher values. In PCMark05, the differences were more or less around 1 MB/sec in all tests.
At the time of the review, the price of the WD2500JS SATA II was US$95, while for the WD2500JD SATA, US$86 and $121.50 for the WD3000JD.
(Prices from pricegrabber.com).
So, is it worth investing in a SATA II HDD? Well, according to the above prices for the WD2500JS and WD2500JD, the answer could be yes, if 250GB is enough for your needs, since you can pay a little more and purchase the WD3000JD with 300GB, with few differences in performance. Also, keep in mind that currently, there isn't a SATA II HDD with a capacity larger than 250GB.