1) A larger SSD is faster than it's smaller Brother. ie a 128 gig BrandX is faster than the same make/model 64 gig.
2) Raid 0 does not really improve much on Boot time or program load. What raid 0 does do is Increase performance when large data structures are written/read as these rely on Sequencial performance which raid0 does Improve. raid0 does little to none for small file random read/writes which are important for Boot and program load times.
3) On Agility III (I have two 120 gig Agility IIIs), This SSD performs NO better on SATA III as it does on SATA II (identified in a review, and I verified on My system). My take - Agility III is a SATA II SSD in a SATA III dress.
BOTTOM line - The vertex 4 is by FAR a better choice as opposed to the Agility III. However I would select the Samsung 830 as it seems to be less progmatic, and I personnaly DO NOT buy OCZ
PS my normal recomendation is for: Curcial M4, Plextor M3/ M4, Samsung 830 - The New Samsung 840 - WHEN it comes down in price.
Also have 3 M4s and three Samsung 830s.