Most people either use something like
Parallels - seems like a simple out of the box solution to use windows and mac at the same time with low need for configuration.
Virtual box or alternative - lets you install windows but you do need to do more configuring to get things working well
VPS/Server - simple and effective you simply use RDP, which mac supports and remote into a windows server. An advantage here is that you can leave it running and come back to it from any machine or even a tablet etc... and it just always runs with its own dedicated resources. Its also in a data center with a quality connection so good speeds.
I have several windows machines in my house and I don't use gsa on any of them, all my copies of gsa run on servers in data centers. Almost all my copies of Scrapebox run on servers and all my copies of captcah breaker runs on servers, its an effective method.
Depends on your budget I guess.