No-worse-than-my-Rift is very reasonable. There is continually a lot of people setting themselves up for disappointment, however - not just here - so now and then I can't help but feel a reality check is in order. :7
A significant part of optimising a game amounts to limiting the amount of stuff (and how complex that stuff is to render) that is thrown onto the screen at any one time, and with a scant few exceptions, most of which are very rarely implemented, that is essentially the only thing that differs, performance wise, between a made-for-VR title, and one that has been retrofitted for VR: It uses simpler graphics (clever art direction can as always reduce the perceptual impact of this), in order to hit 90fps with two viewports, where a game targeting monitor/TV does not only only need to render once per frame, but can also often get away with framerates down to the thirties, and even dipping into the twenties.
Developers have already used every trick in the book to coax performance at a given "bling level" out of their games without VR -- there is no magic spout that can be opened, in order to make the drawing of a given picture suddenly go twice as fast, only because it goes to a different display unit.
I actually had an argument, last year, with a fellow who was absolutely convinced Fallout4 VR would run like Usain Bolt, due to optimisations for VR, whatever he may have imagined those would entail.
On the contrary, as it happens; There are a lot of dirty little optimisation tricks that you can easily overlook when playing on a flat screen, but which fall down when seen in stereo, and just to make sure every road is an uphill one, all that eyecandy that one carefully rations, for performance, one really really do want in VR; Texturing that holds up to rolling one's detatched eyeballs across? -Absolutely! Realtime dynamic lighting and unlimited highres shadows, as well as perspective correct reflections? -Yes please. Actual dense geometry, or at least parallax mapping, so that a rough stone wall does not look like it is painted onto drywall? -Well that goes without saying, as does distant land LOD that looks somewhat like its close-up counterpart. Physics on everything, yaay!
Hopefully sooner, rather than later, foveated rendering will help with much of this. :7
Given the respective FOVs and render targets of the devices, I expect a tiiiny bit better resolution out of the 8k, than the Rift CV1 (actual rendered stuff - not physical display pixels, and quite possibly more of an improvement horizontally than vertically, due to screen utilisation and video scaling matters). This means that if you are supersampling today, in order to make things look acceptable, it is quite likely you are going to want to do it with the 8k as well. This on top of the fact that there is 2.84 times as many pixels to render, to begin with.
As for things running better on Rift today than at launch; I don't know whether this is in reference to developers having learned their optimising, over time, or changes on the Oculus software stack side, but in the case of the latter; The compositor is what it is, and was always tight and with little overhead; The big difference lies in mitigation strategies for when rendering can't keep up, but if one get to the point where more than a handful of frames have to be synthetsised per minute, one have already failed, as far as I am concerned. Some people claim that fake frames look close enough like real frames to them, that they don't really notice... Those people are blind, I suppose - they also claim that they can "forget" and not notice the screen door effect and "god rays" in the fresnel lenses, not to mention binocular rivalry...