Not sure why your usage went up after upgrading, assuming all the old settings imported correctly. It shouldn't have.
Yes, direct to disk for each camera yields big CPU usage savings. You need to be aware that when you use direct to disk, you need to make the cameras embed their own timestamps, as the timestamp
Blue Iris can add for you will not be part of recorded video.
Also if your CPU supports Intel Quick Sync Video, you should enable hardware accelerated video decoding in Blue Iris options on the Cameras tab (h264 decoding only, do not use the "VPP" option), then restart Blue Iris to make it take effect.