My opinion on this is that the issue is not bottlenecking, it's actual performance. Is your setup not giving you the performance you need/want? If you're getting the performance you want, then what difference does it make if there's a bottleneck?
By the way, there will always be a bottleneck. If you upgrade component A, now component B is the bottleneck. If you upgrade component B, now component C is the bottleneck. If you keep upgrading things, eventually component A will be the bottleneck again.