Now that took a while

nicstt

I was trying to get rid of some artifacts/graininess in some shadows. so left it rendering over night. I use a 980ti and a 970.

I stopped it at 94% converged - ish.

Iray INFO - module:category(IRAY:RENDER):   1.0   IRAY   rend info :     CUDA device 1 (GeForce GTX 970): 7319 iterations, 76.477s init, 33030.323s render (over 9 hours).
Iray INFO - module:category(IRAY:RENDER):   1.0   IRAY   rend info :     CUDA device 0 (GeForce GTX 980 Ti): 30323 iterations, 66.560s init, 33039.987s render

I was surprised at the time, but also curious as to why the 970 would only contribute 25% towards the render; admittedly it is driving the monitors, even so, with nothing happening, it was a surprise.

My point, if it is consistent, is that although it has half the cuda cores, don't expect the performance gain to translate to rendering from the card you're using for display; other factors will come into play.

prixat

Its probably the Memory Bandwidth (plus other advances) on the newer processor, which is approx. halved on the 970.

As well as having half the number of cores, the 970 is also calculating at half the speed.