...G2R5 is the retail package, with Intel label and logo, instruction CD, 3.5 to 2.5 in. adaptor and manual.
...G2C1 is the "OEM" package, in a plain box and without the CD, adaptor or manual (but with an Installation Guide).
...G2GC, i suppose, is the SSD itself, wich is the same for both packages. At newegg there is a US$ 30,00 plus for the retail price compared to OEM.
So, it is exactly the same SSD in different presentations and you can use one piece of each to make a raid 0 configuration.
By the way, G1 and G2 are the first Generation (50 nm, no TRIM support) and second Generation (34 nm, TRIM support in W7) of Intel SSD's; G2 is the SSD of very preference in a buy.