Test kits are a great investment and IMO the best way to find the right spine. When ordering a test kit, make sure each arrow is marked with its actual spine, not just a range like 55-60. For example, you can have two arrows each in 55-60 and 60-65. It is possible to get four arrows that are 60 lb spine. At best, you never really know what you are shooting.
I like arrows spread out in two pound spine increments, that way you know exactly what you are shooting and what will work best in your setup.