KVM on CentOS 7 - sluggish performance with Win10 Guest

Hey all,  I've been running a Win10 Pro (64bit) guest for some time now.... and originally it was pretty snappy and I had no complaints. Somewhere in about the last 3-6 months I've been noticing sluggish performance -- but not overall. The system is mostly remote so I do a lot of my admin via RDP or the local console with the KVM Manager. I recently did a complete fresh install of Win10 Pro (1909. Previous install was 1607) and both show the same problem. The ONLY real thing running on this VM is Milestone's surveillance system (standalone host). Where I see the "sluggish" is: Connecting to milestone mobile server (either through web browser or client). for the small number of cameras, the connection spool up takes like 15 seconds which is noticeably longer than other systems I have set up with more load/tasks in terms of cameras. This used to be speedy and fine. The other place I see sluggish operation is on the desktop doing some typical tasks and seeing "not responding" in the window of the task that goes away - but should it ever appear to begin with? The system is a Supermicro motherboard with Dual Intel(R) Xeon(R) CPU E5-2640 v4 @ 2.40GHz w/64GB The Guest is provided with 20 cores in a config of 1 CPU, 10 cores - 2 threads per core. There are dedicated NICs (dual NIC card) attached to the system via macvtap (and are not used by CentOS in any way except to pass through to this Guest) I'm using QCOW2 for the base OS. The storage volume for video are raw devices. Once a process is running, performance seems fine... it seems to be starting processes or something. I'm not sure -- and I'm not as intimate with KVM/libvirt as I'd like to be yet. So I'm wondering if there's any performance tweaks I should know about. I've read about using .img vs .qcow2 already. I'm using virt-io drivers to some extent.... but is there anything else I'm missing? Thanks in advance,  -Ben