I would recommend just running with one 128GB drive versus two drives. There will be no performance benefit with running two seperate drives. The only benefit would be having your personal files on one SSD and the OS on the other, so if you had an issue you won't loss the data. However, I would recommend using a standard 1TB drive (Samsung Spinpoint F3 for example) for those purposes.
Generally speaking, as size goes up so does performance. NOT by a big factor and not sure it would be noticed in day-to-day operation.
I'm not a gamer, but based on reading here at Tom's. FPS do not improve when program is installed on SSD, Maps will load faster.
My vote = The 1 128 gig.
If your looking at performace, take a look at performance/reviews. C300 was the first on the block with SATA III SSD, but performance wise, newer ones are better and faster.
When comparing the C300 (SATA III) with the SF1200 contoller based SATA II SSDs - Went with the Phoenix Pro and have NO regreats. Next SSD will probably be one of the newer SATA IIIs, But may still opt for a large sata II as prices are coming down on the sata IIs.not even considering the C300 - But that is just me.