I doubt you will enjoy using a 5’x5’ mpcnc it will be significantly less rigid than the recommended build size. You might want to at least cut one axis down to 2’.
We are the same community of people using both machines. They use the same exact hardware and software. The lowRider was my answer to the demand for a machine as large as you want to build. No one has asked for printed or cut parts for it until two days ago. I can print and cut parts and will offer them very soon. I have invested a lot of time and money into the other hardware, but demand has been so low I have spent my time on improving the website and the behind the scenes stuff.
You can build it any size you want, just know you will need to take extra care to get CAM settings correct or you will not get desirable results.