Thanks for the reply. Just wanted to follow up that I am using a DS-7616NI-E2/8P NVR viewed with the IVMS-4500HD app for Android. I am also using Blue Iris.
I found an app called Tiny Cam Monitor which works reliably with ONVIF/HikVision cameras and supports hardware H.264 decoding. So running on a tablet with Wi-Fi it produces nice quality, smooth framerate. Seems like a pretty complete app.
Presently I have the cameras joined to it directly, bypassing the NVR, using UDP. No buffering/sync issues anymore. I will try reconfiguring it through the NVR again later and see what that yields.