Agreed with aboved.
I personally use high rpm, low latency 2 drive raid 0 for ONLY windows page file and all other temp (setting windows temp folders, browser temp folders, download temp folders, etc) Os drive is strictly os and program files only. since only read is performed raid 1 wins. more drives in raid 1 = faster read.
You can add drives to the raid 0 for added performance, thats why i only use small drives. 2x 36gb u320 scsi 15k cheetahs. you can always go the consumer route and do wd velociraptors or even 3+ older raptors should get you the same perfomance.
As far as degredation goes, really depends on the controllers/software.
If you have good hardware, then all thats left to fix is the software. lol.
Most decent controllers will have functionality to maintains your arrays but some require user intervention (software based chips whether you have an amd or intel board with intel, lsi {nvidia}, jmicron {gigabyte likes to use these})
I've noticed some users on this and other forums complain of slow raid 5. thats not the hardware but the user who did not set it up properly. Even onboard fake raid (software) has the capability of 100mb + through-output.
Helps to match stripe size with drive format sector size. <-big hint. less cpu calc required to break down data to match stripe size . (durdur)
Please install the software from intel (intel matrix storage manager) nvidia (nvidia chipset drivers), or what ever board you have. Softraid requires software to maintains performance. dont skimp on it because your nlite'd xpsp3 auto installed drivers and it "works"
Windows wdm drivers are also a joke and waste cpu.