The new GTS isn't a whole lot better then the GT (barely scrapes 15-20% improvement), but if your dad offered to pay for it, then heck, get it (finding it in stock might be a bit hard though)
I personally wouldn't recommend a RAID config, they *might* give you a small performance boost, but I highly doubt it'll be anywhere near anything really noticeable to the point where you'll be like "HOLY BOOGERS It's wayyy faster!!!"
At most you'll see a 5-15% improvement on load times, or something equal to a few seconds, bjut nothing more then 20seconds really on games. Windows might load a bit faster, but if you want to do that you can do it in a myriad of other ways then hardware upgrades.
The 2Gbs more of
RAM also probably won't do a whole ton (I'm assuming you're running in 64bit). Honestly, if you performance, memory running in dual channel will bring you a much higher performance increase then throwing in 2Gbs more and sacrificing the dual-channel on the 2Gbs. Just my thoughts, on the other hand, if you aren't looking for performance, then I geuss 4x 2Gbs is ok, though I don't really see a point to having 4Gbs of
RAM, it's pretty superfluous to have anything above 2Gbs.