[spaghetti]

I don't know how much is a lib in kilograms (european smartazz) but the more you split/divide the weight, the less pain you'll feel, as weight is not concentrated on a single area of your lower back.
Ankle weights are a very useful piece of kit too for spearfishing. I use 2 x half kilogram.
As a general statement, especially in shallow water, a correct weight set is 50% of all you need for successful spearfishing.