I have a current model MacBook Pro Retina 15". I have Windows 8.1 Pro installed to an external USB3 SSD, which is set up as a Boot-Camp drive and works astonishingly well. Note: This is tricky to do, and it probably requires a relatively new-ish Mac to work. There's a website that details how to do it here:
http://bleeptobleep.blogspot.com/201...-external.html
I have SH4 Wolves of the Pacific, and will try to install it and let you know how it works out.