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Out of curiosity, what case are you using? Also, a RAID array is not recommended as a backup. If your array is striped, one drive failure will result in all your data being lost. The failure rate doubles with each additional drive. A mirrored setup doesn't fair much better, because if data becomes corrupted on one drive or you happen to pick up a virus, the same will happen on the others. Personally, I back up important files on flash drives, external hard drives, and DVDs. Another option is using a "cloud" drive, depending on how strong your Internet connection is.
GPU: Intel HD3000 (onboard). This will be good enough since you aren't rendering 3D images. The UD3H motherboard is one of the few with a DisplayPort out, supporting up to 2560x1600 resolution. Otherwise, you will have to get a discrete GPU.
That 128GB SSD will have room for your OS, Office, CS5 and lots of other productivity applications. And yes, they will all load noticeably faster. You will want to change the location of certain folders (Documents, Pictures, Videos, Music, etc) to a mechanical HDD so your SSD won't get filled.
I forgot to take overclocking into account. You can do up to around 4.0 GHz on stock cooling safely. Any more and you will want an aftermarket cooler. Overclocking is also CPU (and case) dependent, but generally speaking, a Hyper 212+ will get you to 4.5 safely and a Noctua NH-D14 should get you into the high 4's. You just need to make sure your case is wide enough to fit them. I specified the low-profile RAM modules so that they would fit under virtually any tower-style cooler.