Once everything (and I mean everything) in your PC can't be upgraded any further than get a Raptor. Until then I
will not recommended them.
The 3Gb/s only benefit the user for burst speeds. HD don't maintain the 1.5 from SATA I.
Now for HDTACH:
2 74GB raptors in RAID0:
I think this is 2x 250GB Seagate drives in RAID0
Single 36GB raptor:
Single 74GB Raptor:
Basically these show the raptors having faster access times for reading lots of small files where as a large file would be faster on a RAID array or a single larger hard drive (just). Go for what you want but as I said I think they are a waste of money.