The severe frame drop when dropping out at a station is a bug which hopefully will be fixed in 2.3.
You won't be able to run VR on Ultra and get 90FPS for £350. From what I've read the 1080s are struggling to do that (they can run Ultra but it means making use of ASW so you end up running at 45FPS...a 1080 owner will correct me if I've got that wrong). A Titan XP should be able to do it
I believe the only AMD cards that can currently use ASW are the RX 400 series so RX 480, but IMO this wouldn't be a significant enough upgrade from your 290X to justify the spend and the 480 is distinctly mid-range.
To give you something to compare I have a 390X 8GB and I either run with HMD IQ at 1.5 (to sharpen the image, mainly the text) and everything on low (to keep judder down) or with HMD IQ at 1.25 and a few of the other options at low/medium (I find in VR that the difference with the graphics options is much less noticeable compared with 2D). The frame rate rarely stays at 90FPS unless I'm in empty space but ATW kicks in and keeps things smooth. Actually FD did some optimization with 2.2.03 so I need to try turning a few options up.
I'm waiting for the Vega cards but they won't be cheap (FWIW I have a Freesync monitor so will probably stick with AMD and I refuse to pay the current Nvidia prices).
EDIT: one option is a lower-spec 1070 which seem to start at around £390 at the moment but again don't expect Ultra at 90FPS.