You can potentially save yourself a lot of grief if you figure the center shot. Take a string and tape it to the exact center of the limbs well above and below the shelf. Then looking at the side plate area head on, and the string will show you a much better visual of your amount of center shot. In addition to the actual bow weight, this factor (amount of center shot) will have a tremendous effect on required spine.
Some loose guidelines for you, for a 28"-29" arrow.
Less than cut to center - often at or below marked bow weight.
Cut to center - often at or slightly above marked bow weight.
Cut well past center - well above marked bow weight, typically 15-20 pounds.
Arrow length and point weight will cause you to tweak this a bit, but I think you'll find the above guidelines pretty close for a typical set up.
Hope this helps, Tim