Nowhere in your post did I see the word 'performance' .
They're going to be the same, unless you are able to perfectly somehow get the exact right condtions to take use of the 3.0gh/s bandwidth SATA2 offters...not much of a difference besides smaller cables really.
But to reply to what you SEEM to be trying to say: why buy something that has limited potential when for the same, or sometimes LESS cost, you can get something with a higher speed potential?
SATA drives are cheaper nowadays, and are generally having a larger cache (which contributes to the larger speed boost...as well as most higher RPM'd drives are SATA too).