Time for a New Computer. Plus some things explained ?

[Calibound88]

Sorry If this post is tl;dr, but if anyone could just briefly answer any of the questions (not expecting full detail descriptions) or suggest better (quality to cost ratio) products it would be much appreciated.

I'm building a computer mainly for gaming (Starcraft II), streaming and schoolwork.
Resolution: 1920x1080 (main) + 1080 x 960? (secondary)

Budget apprx : $700

Also post is x-posted in /r/buildapc for more input.

CPU
Newegg.com - Intel Core i5-2400 Sandy Bridge 3.1GHz (3.4GHz Turbo Boost) 4 x 256KB L2 Cache 6MB L3 Cache LGA 1155 95W Quad-Core Desktop Processor BX80623I52400

• Last CPU I owned was an LGA 775 socket. Why is there now a 1155 and 1156 socket? Which one is phasing out/newer? And are both still being produced?
• Also is there a significant difference between the i5-24xx and i5-25xx. Or is the later factory overclock. Assuming not worth the upgrade if true?
• What happened to FSB? And...lol wut...why is there integrated graphics in my CPU?
• So if there is no FSB, what is today's equivalent?
  
• The phenom II x4 look really cheap now. Is it worth the buy?

Motherboard
Newegg.com - GIGABYTE GA-Z68P-DS3 LGA 1155 Intel Z68 HDMI SATA 6Gb/s ATX Intel Motherboard

Ram
Newegg.com - G.SKILL Ripjaws Series 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model F3-12800CL9D-4GBRL

• I still assume that any more than 4gb is unnecessary for my needs? Or have we transitioned into the realm of 6-8gb.

Hard Drive
Newegg.com - SAMSUNG Spinpoint F3 HD103SJ 1TB 7200 RPM 32MB Cache SATA 3.0Gb/s 3.5" Internal Hard Drive -Bare Drive

Case
http://www.newegg.com/Product/Product.aspx?Item=N82E16811129098

GPU
Still Looking. So many New Ones.

• No huge difference between the GTX 460 and GTX 560 I presume? Both are an upgrade from the 8800gtx?

PSU
http://www.newegg.com/Product/Product.aspx?Item=N82E16817371016

 

[NeXuS1]

IF you could stretch your budget a bit to get the 2500k you're set for a while.