Bottleneck is thrown around a lot, but it is not the end of the world. While an AMD CPU does tend to bottleneck recent high end GPUs, it is only a small percentage performance lost. Think like 10-20%, which would put you and your friend on a pretty even playing field.
When you already have parts and aren't considering upgrading everything, just get you can, don't go overboard with something like a Titan XP, but reasonable. Almost without exception there will be gains somewhere in the system by adding any faster part. (Except maybe large ram capacities, but then you could do things like SSD cache or RAM drives with it)
AMD chips tend to post similar maximum FPS with the same GPU. Where you see the difference is in the minimum and average. That is when the GPU has to wait on the CPU for data. That would apply to most GPU bound titles. CPU bound titles is another matter, games like GTA 5 show much lower numbers due to the lower IPC of AMD's architecture.
Hopefully that all changes when AMD releases their new line and we have some decent choices again.