Hi Trevor,
Welcome to the bbs mate
I have used both the NS156 and and currently the Paladin 390 and for me the paladin is better suited to the ranges that you have specified, it is much heavier than the 156 and I can recommend the venom air cylinder for the HW100 which will shave approx 1lb in weight and help to bring the balance of the rifle closer to the shoulder.
The 156 has a circular ret which many people don't like and benefits from the use of a additional illuminator if your wanting to pick off bunnies at 45 yards.
The Paladin has a standard cross hair ret and a far more powerful illuminator. it will focus down to approx 7 yards so it is ideal for close range ratting
The Paladin is far more expensive than a 156 though!
You will need a weaver to dovetail adaptor rail or Uttings sell a couple of small blocks that do the job perfectly well.
Alan.