AFAIK, it's long been known that render times take a big hit when using displacement, since it's calculated at the time of rendering.

As for the jaggies, a larger map, and/or a lossless map would help considerably.

I use displacement a lot, generally when the mesh would be stupidly high poly if I didn't.  It ain't all things to all people but it does have its uses.  

 

Coppula eam se non posit acceptera jocularum.

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