try NNEDI3 image doubling combined with SuperRes "upscaling refinement" (with all SuperRes sub-options unchecked). I like the combination, it makes images extra sharp and detailed. SuperRes sometimes even "fixes" some problems NNEDI3 by itself might still have. If you still want a bit more sharpness than NNEDI3 + maxed-out-SuperRes provide, then try adding a bit of "crispen edges" in "upscaling refinement". Or alternatively to "crispen edges" you can try "AdaptiveSharpen" with anti-bloating, which might be slightly higher quality, but also higher GPU cost. I think this should put the Darbee to shame, especially because "upscaling refinement" is applied in the upscaled resolution, while Darbee sharpens before scaling, which produces lower quality.
The 1080 is really mighty, but if you unexpectedly run into performance issues, try using super-xbr (with activated anti-ringing) for chroma upscaling instead of NNEDI3. Almost the same quality with much lower GPU cost.
As a projector user you may also want to look into the "zoom control" settings page. This page, combined with the projector device's "screen config" page allows you to fully automate CIH, CIW and CIA setups. madVR will then automatically detect black bars which are hard coded in Blu-Rays (e.g. Cinemascope movies) and zoom the image to fit your screen. Alternatively, madVR can also remote control your projector (only works for JVC and Sony projectors with lens memory and IP control capability) to automatically activate a specific lens memory, depending on the movie aspect ratio. You can also define how you want IMAX Blu-Rays with switching ARs to be handled (e.g. always zoom in, always zoom out, always zoom half way, or dynamically adjust AR). Whatever your front projection setup needs are, madVR should be able to automate everything. You may have to use settings profiles for best effect. E.g. when using an anamorphic lens only for scope movies, you will need to create two different "screen config" settings and auto switch between them with the "profile auto select rules".