Here are the recommended VirtIO drivers v0.1.173-9 for Windows 7 as a VM under ProxMox.  These are the most stable drivers, including working memory ballooning.  They are also the last version of the signed virtio scsi driver, which you need if you are doing a fresh install using the vioscsi for the hard drive.  See the long description for links to forum posts with additional information.

https://forum.proxmox.com/threads/windows-7-64-bits-signed-virtio-drivers.27883/

https://github.com/virtio-win/virtio-win-pkg-scripts/issues/40#issuecomment-1565538797