Do water cooling hv a great impact on ability to OC(CPU & GPU) ?

Generally speaking, the better you can cool your hardware, the higher the overclock you can achieve. This is extremely true of the CPU. Ive never actually OC'd my GPU so I cant talk too much on that, but yeah it has a huge impact.

also, please take some time to read through the watercooling FAQ thread, you will learn a lot about watercooling pro's & cons.

Almost every question above, it's purely specific to your setup and ability. Not all overclocking is limited by heat...most of it (90%+) is user ability/knowledge and specific hardware used and actual binning of those components.

er another question for u.
typical water loop sert up for fx8350 and 2 gtx 670 need how many radiator ?

Preferably you'll want to run a dual loop setup. But if your gonna run a single loop, you really should use 2 RADs and make sure your pump is strong enough to handle it.

i going to use 1 x 240mm & 2 x 120mm in a phantom 410 case will it fit??

It may fit but sufficient it will not be, read sticky, calculate TDP, work out required radspace
Moto

+1

yes it does

FX8350 = 125 tdp and gv it 75 tdp for OC headroom (200 tdp)
2x gtx 670 =340tdp OC headeroom +60 tdp for both (400 tdp)

according to http://skinneelabs.com/assets/images/Radiators/XSPC/RX3...
with only 3 x 120 radiator at 600 tdp & with yate loon D12sl12 at 1000rpm temperature delta will be 17'C
with 4x 120 radiator it should be lower then that.

For pump, according to http://www.overclock.net/t/1108918/what-can-my-pump-han...
Radiators: 3x 0.20 PSI each = 0.60PSI
CPU Block: 1.1 PSI
GPU block: 2x 0.9 PSI = 1.8PSI
Fittings: 0.3 PSI for the entire loop
Tubing: 2 x0.5 PSI per meter = 1PSI

Total PSI 4.8PSI
i'm going with MCP35X Stock: 6.52 PSI

i should be ok ?

As a rule you should be aiming for a Delta of 10'C,
get better if you can but 10 is the normal W/c target, I'd be surprised if the Yates didn't need to run at full speed to get you cooled on a single 360,
More normal for a Cpu/2xGpu loop is a 360+240 set up although a cooler and quieter running loop would be 2x360's
with three blocks and two rads I'd definitely be going for the Mcp655 or Pmp500 level pumps, flow rate matters  
Moto