So where does this https://developer.nvidia.com/sites/default/files/akamai/gameworks/Frustum_Trace.jpg fit into what you just described. Also the how does the irregular z-buffer fit into this?
That's afaik, the ray vs triangle intersection test. You construct your frustum as in the jpeg then test if the onscreen pixel is inside that frustum. Don't remember what the irregular Z-buffer was for, as I glanced through the paper and concluded Sebastian's "virtual shadow mapping" (about 3/4ths of the way down) would serve something similar in terms of image quality while doing so a lot faster.
If you're really going for some "make high end PC stuff useful" as Joe-J suggests I've found just having everything be scaleable in the engine is a good idea anyway. That way you can turn things (SSR/SSAO samples, shadow map res, g-buffer quality, LOD distance/quality, HDR buffer quality, etc.) down and/or up as needed to hit any platform and target framerates.