But it's not either/or. The GPU will be priority, once it's maxed out , transcoding will fall back to CPU. So you'll have both.
To add to this, when he says "maxed out" this means one of the other video cards that have a stream limit like the 1050. Once those two streams are in use and you do a third it will use the CPU... However the cards with unlimited streams like the P4000 will just keep taking on streams until it starts to bog down causing skipping... At this time it wont roll over to the CPU if the FPS starts to drop too low.. I would like to see that feature.. :-)