Need suggestions of this Build

Hi to all,

I am looking to upgrade my system soon and have put together some components I would like to add or upgrade from my current rig.

The 3 things I want to upgrade are:
1. RAM
2. CPU
3. GPU

My current system is below:
PCPartPicker part list: http://pcpartpicker.com/p/8cZ3WZ
Price breakdown by merchant: http://pcpartpicker.com/p/8cZ3WZ/by_merchant/

CPU: Intel Core i5-4670K 3.4GHz Quad-Core Processor ($233.99 @ NCIX US)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($28.66 @ Amazon)
Motherboard: Asus Z87-A ATX LGA1150 Motherboard ($124.99 @ NCIX US)
Memory: Corsair XMS3 8GB (2 x 4GB) DDR3-2000 Memory ($114.99 @ Newegg)
Storage: Samsung 840 EVO 120GB 2.5" Solid State Drive ($99.99 @ Best Buy)
Storage: Samsung 840 Pro Series 256GB 2.5" Solid State Drive ($167.98 @ OutletPC)
Storage: Western Digital WD SE 2TB 3.5" 7200RPM Internal Hard Drive ($132.99 @ Amazon)
Video Card: Sapphire Radeon HD 7950 3GB Video Card
Case: Rosewill BlackHawk ATX Mid Tower Case ($89.99 @ Amazon)
Power Supply: OCZ ModXStream Pro 600W 80+ Certified Semi-Modular ATX Power Supply ($87.37 @ TigerDirect)
Optical Drive: Asus DRW-24B1ST/BLK/B/AS DVD/CD Writer ($16.99 @ Newegg)
Total: $1097.94
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2014-09-22 11:38 EDT-0400

This is what I am looking to upgrade to [In Bold]:
PCPartPicker part list: http://pcpartpicker.com/p/rDpYf7
Price breakdown by merchant: http://pcpartpicker.com/p/rDpYf7/by_merchant/

CPU: Intel Core i7-4770K 3.5GHz Quad-Core Processor ($333.99 @ NCIX US)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($28.66 @ Amazon)
Motherboard: Asus Z87-A ATX LGA1150 Motherboard ($124.99 @ NCIX US)
Memory: Corsair Vengeance 16GB (2 x 8GB) DDR3-1600 Memory ($159.99 @ Newegg)
Storage: Samsung 840 EVO 120GB 2.5" Solid State Drive ($99.99 @ Best Buy)
Storage: Samsung 840 Pro Series 256GB 2.5" Solid State Drive ($180.98 @ Newegg)
Storage: Western Digital WD SE 2TB 3.5" 7200RPM Internal Hard Drive ($132.99 @ Amazon)
Video Card: EVGA GeForce GTX 970 4GB Superclocked ACX Video Card ($339.99 @ Amazon)
Case: Rosewill BlackHawk ATX Mid Tower Case ($89.99 @ Amazon)
Power Supply: OCZ ModXStream Pro 600W 80+ Certified Semi-Modular ATX Power Supply ($87.37 @ TigerDirect)
Optical Drive: Asus DRW-24B1ST/BLK/B/AS DVD/CD Writer ($16.99 @ Newegg)
Total: $1579.93
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2014-09-22 11:40 EDT-0400

This is intended to be a gaming PC and I will be playing MMOs for a majority. Prior to building my first rig, I thought GPUs were the most important part and did not invest is a I7 so I guess I am paying the price for it now since its only been less than a year since I upgraded to the I5.

Here are my questions:
1. Is the up to the I7 really needed to have a smooth FPS and no bottle necking while playing any MMOs?
2. Should I stick with the GTX 970 or pay the extra for a GTX 980?
3. The current wattage is way under the 600w power supply I have, should I upgrade this as well as I may have 2 GTX 970s if I don't get the 980 and would this is overkill?
4. Is there anything else I should be prioritizing to upgrade to improve performance?

Any input will be very helpful.

Thanks in advance.