First a little note: you really should use ATTO to test the throughput on RAID-volumes, not HDTune which only uses a queue depth of 1 to access the RAID: that means both disks in the RAID are not used at 'full throttle'. ATTO on the other hand, will test on the filesystem. So all optimizations the filesystem has (write buffering and read-ahead) will get used.
HDTune on RAID-arrays can provide wrong (lower) results.
But more important than the maximum MB/s you can get, the throughput, there is also the IOps performance of your array. Those cannot be tested easily though some proprietary tests (PCmark/Vantage/iPeak) exist that try to mimic real applications such as Firefox or Microsoft Office to see how well the storage device performs when simulating the I/O behavior of these applications.
RAID0 in theory could improve both IOps and throughput in the same degree: they double with each increase in disk count: 2 disks in RAID0 can provide up to 200% increase in IOps and throughput. But this is theory, in reality - especially on Windows - many performance barriers exist that get the most out of your RAID-array. One important one that limits IOps performance is called a 'stripe misalignment'. This is because Windows partitions in a way that causes one 'filesystem block' to encompass two or more stripe blocks. In simpler terms, the filesystem and RAID-system are not properly 'aligned'. This in turn, causes one I/O operation to be handled by two or more disks in your RAID0 array. Whereas it would be better if each disk in the array can process its own I/O operation. In this case, your RAID-array can process 4 I/O's
simultaneously instead of one at a time, which is very much faster indeed.
So that's what i meant with Windows systems being 'crippled' when using striping RAID storage. This does not affect RAID-1 (mirrors) or JBOD arrays though.
As for your raptors: while they aren't faster with throughput (MB/s) they are faster with IOps. And when you launch applications or games, or other realistic non-sequential I/O, the throughput really is not that important. What people call access times is only part of the equation; what actually counts is howmuch I/O operations per second (IOps) these disks or arrays can process. SSDs are masters here, thats why they boot so fast and open applications so fast; their random read IOps can be about 30.000 I/O's while a fast HDD can perform only 100-200 per second.
In other words, while your raptors will be slower in throughput, they are better suited as your system disk than ordinary 7200rpm disks. You should keep the raptors, maybe repartition with some help of google by correcting the stripe misalignment, and use your big drives as 'data drives'. Not to install applications on, but to store large files and downloaded data, plus backups etc.
Getting a second 1TB drive (i recommend WD Green 1TB WD10EADS) allows you to fully backup all important data you have on your other 1TB drive and also parts of your system drive (the two raptors).
You can download ATTO here:
http://rapidshare.com/files/214298798/ATTO-256.exe.html
(this is the newer '256MB' version; the original only goes up to 32MB)