My 2 cents: Just use what you've got for a while you'll eventually figure out what makedodt sense for you. The factory configurations are usually good, balanced, get used to the feel of that before changing things.
For me, moving to a shorter lighter speargun became the obvious next step. Then getting an additional longer light speargun, for clearer conditions.
If you find you need more range a longer Speargun usually makes sense. Faster tracking? A lighter, slimmer, smaller Speargun might suit. Insufficient penetration? Then perhaps a double band or roller speargun. Trouble loading? Double bands with thinner rubbers perhaps. etc..
Get some more experience before changing things. Single band guns are usually quite powerful. If you watch YouTube spearing videos you eventually notice that quite a lot of shots would be fine with just about any Speargun.
If you encounter a lot of those big fish in reasonably clear conditions, you might consider something like a 100cm Rob Allen railguns or roller gun give or take 10cm.