I also have performance issue with lag/jedder/fps on planets too, mainly when moving my head. Using strix GTX970. Before horizons I only played normal elite(non-beta) and aside for the damn SC judder all was well. Now with horizons, performamnce in space is as before and I beleive SC judder is improved, but once getting close to landing on planets -forget about it- not playable!!!
It's funny how some others are having great performance with the GTX970, I don't get it. Maybe it's cpu differences, maybe it's planet-dependant?
We should all do some benchmarking where we pick one planet/moon/port and all test there. That way we can compare apples with apples.
I have the same card, and like you I think the Strix version is less powerful. On my side, I can still run Horizons beyond 75 Hertz with big sacrifices : Turn down SS at 1.0, put everything to low, remove shadows, turn off antialiasing, lower more than half the Oculus quality bar, etc. It's ugly as hell, but most of time everything's running smooth. The Oculus CV1 version will need a much stronger videocard to be able to run at 90 Hertz at higher resolution, I hope Nvidia will sell their next gen card at same time when it become available.