You really need to do some objective measurements, rather than just guessing at what's going on. There's no point spending a ton of money based on a hunch. MSI Afterburner's overlay apparently works with the Rift, so download that, turn on all the GPU/CPU usage stats in the overlay and it should be quite obvious quite quickly where the bottleneck lies in the things you play. There's no such thing as a universal performance bottleneck unless you're pairing wildly-mismatched components (like a Core 2 Duo and a 1080 Ti), so it's important to know how your hardware is performing and interacting in the software you use.