A solid-state drive, having no moving parts to "spin-up" or read/write heads affected by latency, simply must be faster than a mechanical drive -- right? Not necessarily.
Intel's X25-M SSD is one of the fastest solid-state drives currently available. Yet it tied with the 6Gbit/sec. Barracuda XT at the burst speed test (296.6MB/sec.), while the 6Gbit/sec. Caviar Black beat it at 320.7MB/sec. The Intel SSD's average read time of 240.3MB/sec. was better than the XT's 115.6MB/sec. or the Caviar's 112.4GB/sec.
However, with a capacity of 160GB, the Intel SSD holds much less data than the 2TB Barracuda XT and the 1TB Caviar XT. And the X25-M retails around $540 compared to the Barracuda XT's $249 or the Caviar Black's $120.
I'm one of those über geeks from the early days of personal computers. New technology is the shining bauble that immediately attracts my eye and causes an involuntary movement of my hand in its direction. For me there's usually no option. For you, there are several.
I would wait at least four to six months before plunging into SATA Revision 3 technology. That will allow prices to drop a bit and the technology itself to mature. While Seagate has packed the Barracuda XT with 64MB of cache, I believe that 128MB would be better, given the optimal speed of the interface, and I can honestly speculate that Seagate will get here. I suspect that Western Digital will be tweaking the firmware on its Caviar Black as well.
Obviously you can fine-tune the level of performance you can achieve right now in several of the individual test categories by substituting one of the SATA 3Gbit/sec. drives that has the type of performance you need for the applications you're running in place of either of the SATA 6Gbit/sec. hard disks. What you can't do is achieve the overall performance advantage -- which in some cases is admittedly slim -- offered by the 6Gbit/sec. drives themselves.
If you need something right now, Western Digital's SATA 3Gbit/sec. Caviar Black will do the job. It's the Barracuda XT's closest performance competitor among the drives I tested. The 2TB model will cost you about the same as the XT. A 1TB version is available (as well as a 500GB model) for much less, but it will be slower because it only has 32MB of cache.
Also, even with a 32MB cache, the Barracuda LP would be my second choice. At 2TB it's currently priced around $150. You'd end up with the same capacity and reasonable performance at a lower price.
And certainly keep in mind that cutting-edge technology such as SATA 6Gbit/sec. will never get worse than it is now. Typically, all emerging tech tends to get better over time. You have nothing to lose by waiting.