no idea where you're getting such numbers. and as i already said a "bottleneck" does not mean a loss of performance. it simply means that the gpu will not be able to do as much as it theoretically can. the cpu will not be able to feed the gpu fast enough. but it will still be able to ask everything of it that it would for a weaker gpu.
if the cpu can ask for 100 frames per second, then if the gpu can handle 100 fps, then it will do it. if it can handle 300 fps, then it would still put out the 100 fps the cpu is asking it to do and will just be able to do more if asked of it. the cpu is the limiting factor and the gpu can only do as much work as it is asked to do.
on the flip side, if the gpu is too weak then the cpu asking for 100 fps won't happen. the gpu will put out what it can and not be able to do the rest. THERE IS ALWAYS A BOTTLENECK OF SOME KIND IN ANY MACHINE YOU BUILD!!!
don't know what kind of online garbage you're looking at but you do not lose any performance from the system, but rather the gpu just won't be asked to do as much as it truly can. i don't know how else to say this.....