Does any one know about difference between 4Cyl and V6 power sterring ?

I drove V6 KS and seems to be lot smoother than my magna. If its same what issue I looking at ? I have changed oil last year !

Veradas are a smoother ride

Power Steering is same on both. Difference in ride is the spring rates on Verada also the V6 is generally a smoother engine than the 4 pot version.

I have one of each, and the V6 does feel smoother and more stable than the 4, but I put this down to tyre size and brand. You could always put the 15 inch rims off a V6 on your car if you wanted to.

I have 17" Enki Raliart wheel - but is it possible that the motor would have gone worst ?

Noticed when car is turning - it makes a sound as if motor is struggling

Try looking at, and checking all of the steering components. Dry ball joints or failing upper suspension strut bearings will make the power steering pump struggle when you turn, and make it difficult to hold a straight line with the car when you drive it. Did you get the wheel alignment checked when you got the new wheels?