EXTREME lag in ACR actions such as enlarge

I have Photoshop CC 2017 (recently upgraded from 2015) with ACR 9.1.1 (I attempted to upgrade to ACR 9.12 but found that 32 bit image editing in ACR was disabled after 9.10 so I went back to 9.1.1).  I'm trying to edit my Merge to HDR Pro 32 bit images which appear in PS as smart objects and open in ACR.  I don't open Merge to HDR in Lightroom due to the amount of excessive noise generated in the shadows.  Opening the smart object to bring up ACR takes about 60 seconds on average however on occasion it will freeze and I'll have to shut PS down from the Task Manager.   While I'm waiting the for the image to enlarge, the widget monitor shows the CPU at between 25 and 30% and the RAM is between 30-40%. I have a hand tool lag of minutes before anything happens and when I try to enlarge (either with the mouse or with the presets such as going from 50% to 200%) the lag for any activity has so far been as high as 22 minutes (yesterday) however it could take as low as approx 2 minutes for the first use.  While waiting the 22 minutes yesterday, the CPU was running at about 1 or 2% and the RAM was about 25%.  Right now as I type this, going from 200% to 50% is going on 33 minutes and no movement in ACR waiting for the action to complete and the Task Manager shows PS to be 'Running' and not hung up.  I finally gave up and shut it down.  The brush lag is usually just a few seconds.  This is PER action so needless to say ACR is really unusable and my only option is to cancel and exit or just wait it out.  My system is as follows:  ASUS P8P67 Pro motherboard, Intel I5 2500K processor, 16 Gb ram, AMD HD 7970 graphics card and running Windows 7 Pro 64 bit on an Adata 256 Gb SSD drive with 111 Gb free space.  I have a completely clear 500 Gb WD Black drive as my scratch disk.  I have the max ACR cache allowed at 200 Gb on the main photo drive which is a new WD Gold 4TB drive which is only half full.  GPU acceleration is turned offf.   I have 70% RAM allocated for PS but have played with lower amounts.  Both the SSD and the 4TB drive are currently on the motherboard's Marvell SATA III controller however I've also had the SSD and the photo drives on the motherboard's built in Intel SATA III controllers as well.  I have the most current drivers for the motherboard and also for the video card.  I have tried to uninstall PS CC and Lightroom and reinstall it but nothing has changed.  There are days where I can actually work but it's not often. What gives with the lag??  I'm at my wits end on this.