Yeah, two raptors in raid 0... woooo
and for your second question...
They are believed to be slightly quicker, I say "believed" because up to now they seem to be like gold dust. As to if you can or cannot "see" the difference is harder to say. Overall you would "see" the difference with a stop watch, i.e. seek times and the fact that they will tend to have a larger cached buffer,maxtor for example at 16MB, as opposed to the 8MB. Seek times will be generally faster usually -8 or -9 ms. There will be a general speed increase but it will mainly be an "overall" one. Those who will "see" the benefits more than others will be: video editors, some gamers and cad users, simply because the information is more speedily available.
However, in reality as the actual Hard Disk is the same . SATA / IDE / SATA2 are the interface technology names. The interface only handles the data from the disc to the motherboard. The slowest thing is the HD its a mechanical thing the best go at maybe 70mbyte/sec ie 560mbits/sec all well within ATA100 ( 100mbytes/sec) let alone ata133 or SATA150 . Its a bit like having a huge water tank feeding a long thin pipe to your tap you get a trickle ( like Big disk/big cache on USB1) and the mains feed on a 22mm pipe keeps up easily. The other extreme is having a pipe 20foot in diameter to an equally big tap when the tank empties in milliseconds and you have to wait for the tank to fill from the mains via a 22mm pipe ( SATAxx) . In both cases the water main feeds at the same basic rate no matter what .