Well to be honest, EcoMCG put together a better computer for gaming because he has 2 video cards and saved on other parts. To defend my decision however, I put more money into a better cooling solution, and motherboard. everything else is pretty much the same. so to be quite honest get the parts from his list, however, I would change the Seagate barracuda to a western digital caviar black as they are more reliable.
Also, you would like windows 8.1 pro OEM rather than the non-pro version.
here is my setup, whish isn't as upgradeable as yours will be but it gives me amazing results as I play all games on ultra quality with very high framerates.
PCPartPicker part list:
http://ca.pcpartpicker.com/p/2Xwog
Price breakdown by merchant: http://ca.pcpartpicker.com/p/2Xwog/by_merchant/
Benchmarks: http://ca.pcpartpicker.com/p/2Xwog/benchmarks/
CPU: Intel Core i5-4670K 3.4GHz Quad-Core Processor ($254.99 @ NCIX)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($32.50 @ DirectCanada)
Motherboard: Asus MAXIMUS VI FORMULA ATX LGA1150 Motherboard ($319.00 @ Canada Computers)
Memory: G.Skill Ripjaws X Series 8GB (2 x 4GB) DDR3-1866 Memory ($89.79 @ DirectCanada)
Storage: Samsung 840 EVO 120GB 2.5" Solid State Disk ($105.98 @ Newegg Canada)
Storage: Western Digital Caviar Black 1TB 3.5" 7200RPM Internal Hard Drive ($84.99 @ Memory Express)
Video Card: Asus GeForce GTX 780 3GB Video Card ($567.00 @ Vuugo)
Case: Thermaltake VN300M1W2N ATX Full Tower Case ($149.99 @ Memory Express)
Power Supply: Corsair Professional 850W 80+ Gold Certified Semi-Modular ATX Power Supply ($131.25 @ DirectCanada)
Optical Drive: Asus DRW-24B1ST/BLK/B/AS DVD/CD Writer ($18.50 @ Vuugo)
Operating System: Microsoft Windows 8.1 Pro (OEM) (64-bit) ($139.99 @ Canada Computers)
Monitor: Asus VG248QE 144Hz 24.0" Monitor ($294.79 @ DirectCanada)
Keyboard: Razer BlackWidow 2013 Wired Gaming Keyboard ($79.99 @ Canada Computers)
Mouse: Mad Catz R.A.T. 7 Wired Laser Mouse ($79.99 @ NCIX)
Total: $2348.75
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-02-23 19:01 EST-0500)
Also if you don't already have peripherals like a mouse, keyboard and monitor, I suggest leaving at least 400$ of your budget towards that. its up to you completely but there are ways to save some money on parts in the list which you can either save (money in your pocket is much better than money in other peoples pockets lol) or invest into other things like a second monitor or whatever your heart desires!