OK, I understand this but, does this not mean we are basically talking speed here ?
Speed is one factor, memory another. Whereas speed is a twofold issue: The actual runtime cost of tracing more geometry during rendering (and this is also largely dependant on the kind geometry, so this doesn't scale linearly, but also the required preparation. So it's not a simple equation of taking 2x the geometry and receiving 2x rendering time. Memory is even more critical - if the resources don't fit into your memory, there's not that much you can do.
I absolutely understand the urge to get more control of these kinds of things as a "power user" and trust me, we've discussed those options internally for many times as well. We do want you guys to be able to achieve optimal results, but at the same time we want Enscape to stay accessible and straightforward to use in a stable way. We're confident to achieve both of these, getting better and closer with every release. I don't want to exclude the possibility of having more options in that regard in the future, but most likely the focus will remain on further optimizing our "1-click" approach e.g. by leveraging more of the available capabilities based on your gpu, which will benefit all user demographics.