In this case, I think you get what you pay for. NXS and HD5 scopes use a fundamentally different objective lens design.
HD5 scopes use a simple doublet objective lens, which starts to exhibit noticeable image blur when the elevation or windage adjustment from center exceeds about 25 MOA. Whether or not you notice the image blur depends on the bore sight alignment of the rings to the rifle bore for your rifle, and the elevation you need for your load and target range. The 5-25X scope has a max +/-36.4 MOA internal adjustment range, so it's possible to experience a degraded image when shooting long range.
NXS scopes use a more expensive triplet objective lens that exhibits minimal image blur (good resolution) at large elevation/windage adjustment (>25 MOA). The 5.5-22X scope allows a large +/-58.3 MOA internal adjustment range, which is probably why Nightforce used a better objective lens design.
Which scope you need depends in part on the max elevation and windage adjustment that you expect to use. Obviously, reticle selection, turret design, weight, warranty, etc., may also be important factors for you