Am I Cooling Enough for Overclocking

I recently purchased the following from ibuypower

Case(CoolerMaster HAF 922 Gaming Case - Black)
Processor(Intel® Core™ i5-2500K Processor (4x 3.30GHz/6MB L3 Cache))
Motherboard([SLI] ASUS P8P67 PRO -- 3x PCI-E 2.0 x16, On-Board Bluetooth)
Memory(8 GB [2 GB X4] DDR3-1600 Memory Module - Corsair or Major Brand)
Video Card(AMD Radeon HD 6950 - 2GB - Single Card)
Power Supply(750 Watt -- Corsair CMPSU-750TX)
Processor Cooling(Liquid CPU Cooling System [SOCKET-1155 & 1156] - [Free Upgrade] Standard 120mm Fan)
Primary Hard Drive(2 TB HARD DRIVE -- 64M Cache, 7200 RPM, 6.0Gb/s - Single Drive)
Optical Drive(24X Dual Format/Double Layer DVD±R/±RW + CD-R/RW Drive - Black)
Sound Card(3D Premium Surround Sound Onboard)
Network Card(Onboard LAN Network (Gb or 10/100))

With Windows 7 Pro on this, and the intent to do mostly gaming/general use (not much video editing), I intend to give it a basic boost from the MOBO and flash the GPU up towards the 6970 specs. 2 part question here

1) Is this stock cooling system/case (see bold) enough to achieve this? does anyone have any experience with the normal liquid cooling system here?
2) With this system, is thermal paste recommended for me? I'm a bit new to this, so I really don't know the appropriate situations.

Thanks in advance