I'm assuming this is a 3 phase motor? If you do go the vfd route, you need to get a VFD that is rated 33% bigger then the listed HP rating of the motor you want to run.
When I was sourcing a VFD for my 3 hp 3 phase motor for my knee mill the manufacturer said I needed a 5hp VFD to run my 3 hp motor at full power. You lose 33% of the rated horsepower of the VFD because you are only putting in two poles of power and three are coming out. A VFD can be bigger then the rated horsepower of the motor and be fine. But you will likely see poor performance out of one that is too small.
When I was sourcing a VFD for my 3 hp 3 phase motor for my knee mill the manufacturer said I needed a 5hp VFD to run my 3 hp motor at full power. You lose 33% of the rated horsepower of the VFD because you are only putting in two poles of power and three are coming out. A VFD can be bigger then the rated horsepower of the motor and be fine. But you will likely see poor performance out of one that is too small.