In most things you "should" notice a pretty BIG difference. The raid thing is up to you, with raid(0) you can read/write faster but at the same time your seek times go up because the data is spread across 2 Harddrives, also you can use the raid connectors as non-raid IDE headers, giving you support for up to 8 IDE devices, so if you think you might have lots of IDE devices in the future the raid might be for you. If you game alot make sure you have a GOOD video card, this will give you the most benifit for games, if you use flask, the new CPU will be invaluable!!! Upgrading is always give and take (unless you just have cash to burn), decide what you use the system for the most and put your money there, Goodluck!!! and make sure you buy new, refurb at current pc prices is asking for trouble!