I can't see any meaningful difference in fps between 4L and 4R here. Without AI (the one and only correct way to test a scenery), I have about 48 fps on final at 4L and about 52 on 4R, which is understandable, since you have a lot more airport in view at 4R.
However, without knowing what else you have installed, is difficult to tell what's the problem on your system, maybe you have simply too many addons and/or too high settings and, having more airports buildings in view approaching 4R, tipped some kind of memory (ram or vram) exhaustion that caused performances to drop significantly, while it should only drop about 10% in a normal situation.