I am striping two 250gb 7200rpm Seagate hard drives and I'm a gaming addict. I'm currently running a 150gb RaptorX for my OS and all my data/games are installed on the striped drives. The loading time for my games are still pretty poor though and maybe it is due to the current raid config.

For some reason I had it stuck in my head that the optimal cluster size for my raid array would be 128kb, but after reading the helpful RAID FAQ, it mentioned that the smaller size the better (for gaming).

If that is accurate, which I'm sure it is, should I reformat those two hard drives and set them for 16kb clusters?

There are two items regarding the storage subsystem. They are two different things, so don't confuse them:

Stripe size is what you're referring to. This is the amount of data that is written to each disk of a RAID 0 or RAID 5 array in sequence. The default for most controllers is 64K, and this tends to work well for most applications. I would not set it lower than this on modern systems.

Cluster size doesn't have anything to do with the RAID, this is a file system parameter. This is the minimum allocation unit size (i.e. any file less than this size will use at least this much space on the disk). This default is 4K for the NTFS file system, and generally should not be changed unless you have a specific reason to do so.

So setting the stripe size to something larger like 128k would be beneficial or would it have a negative impact?

Thanks for the help

No, the larger stripe would likely not benefit you here. Stick with 64K.