First and foremost, you should buy a new machine. You will get much more runway.
But if you insist, you should evaluate your skills on enhancing an old, no-longer-supported system. For a 4,1 cMP, this can involve updating the firmware; updating the bootrom; swapping cpu's, and so on. If you're so inclined, it can be very satisfying. This forum has hundreds of posts of knowledge and expertise to help you.
The end result can be a system that will run pretty well.
I bought my cMP in 2009. Today it runs Mojave. It's primary purpose is FCPX for 4K editing, supported by CS6.
A note on CS6. I often clean install these apps when I swap disks, from original DVD. The Adobe Updater is somewhat inconsistent, and in my experience does not update to anything close to the last available rev. You need to got to the Adobe ftp site and do some spelunking, and even then ...