First off, Sata III HDDs are a marketing tool, For example if you place a SATA III HDD on a SATA II port it will be Just as fast - Sata III HDD only benifit in terms of burst rate - No real impact on throughput. To answer your question, Raid0 w/2 Sata II HDD will normally be faster than a single Sata III HDD, Assuming thay have simulare spect on sustained throughput, But read on for a better understanding.
On SSDs, They are 20 -> 40 Times faster than HDD and will "blow the doors" off even a raid0 HDD setup when looking at the IMPORTANT 4 K random performance.
s3anister said "it's great for Read speeds but write speeds are actually lower than my Samsung Spinpoint F3." If that is the case He has a problem. Even my older SSDs have MUCH higher 4 K read/write performace compared to My Samsung F3 1 TB drive. Added: and that includes my 120 gig Agillity III SSD, that is slower than his Vertex III
Now on HDD raid0 configuration.
A) Great for Improving Sequencial read /write performance. Unfornatuly this is the LEAST important parameter for a OS + Program drive. How much depends on the Files being read, ie your game maps. If they are LARGE files and NOT fragmented, it will improve the loading of a map. - STILL no wheres near the speed of an SSD.
B) Raid0 does NOTHING for:
.. Improving access time.
.. Very little, to none, on improving the 4 K random File performance. This is what is important to Loading the operating system and loading the initial programs.
PS NONE of the above will improve FPS in game play, nor improve internet broosing, email, or down loading files.
I Have used raid0 for a Long time (including the faster method of short stroking Raid0), and there is NO comparision between Raid0 and an SSD for working with files loaded on the SSD. PS I do Not recommend the 60/64 Gig SSDs, for an OS + program My Min size is 80/90 gigs, with a recommended size of 120/128 gig.