Windows guest virtual PC running abnormally slow

Guest systems running Windows 10 in a virtualized environment run unacceptably slow, with no option in Boxes to offer the virtual machine more (or less) cores from my physical CPU.

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: gnome-boxes 3.26.1-1
ProcVersionSignature: Ubuntu 4.13.0-17.20-lowlatency 4.13.8
Uname: Linux 4.13.0-17-lowlatency x86_64
ApportVersion: 2.20.7-0ubuntu3.5
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Tue Nov 28 00:37:11 2017
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-boxes
UpgradeStatus: No upgrade log present (probably fresh install)