render times - well, it depends from render to render. I have a quad core too. 😉
it is very comparable to other high quality render engines... and the new KT beta I'm testing is much faster than the current official release, but I'm not at liberty to say more right now 😉
on interiors I get great results using the KT preset 'Photon Map Medium +AA' this will generally get me something very nice at 2800px wide in about 30mins. for exteriors I us an unbiased render method called Path Tracing Progressive - this takes some time to clear up, but gives me nearly instantaneous 'preview' renders. So it's great for both uses. Since I'm on a quad, in less than 30 mins I will have great exteriors (assuming lit only with Sun and Physical Sky) Sometimes if the scene is extremely reflection and poly-heavy I can wait up to an hour or two for large px renders. For interiors of extreme high lighting quality and more than 2000px wide on unbiased render preset such as Metropolis Light Transport you can wait up to 12-13 hrs (I start it, go home, come back to finished render the next morning) This is similar to high qual + high res Vray or Maxwell renders.
