The gutters and gutter guards on the market are numerous. I'll let
others comment on them. However, I like the idea of increasing the
downspout size and the gutter size as well to carry more volume.
The gutters and soffit work are trades that are tangent to the roofing
industry. How old is your roof? If you are anywhere ready for a roof
you should consider your whole roof system, which includes the roof
itself, attic insulation, and ventilation including the soffits. It all
works together. An increase in insulation saves energy. An increase in
insulation requires more ventilation to make the roof last and prevent
condensation. The soffits should have increased ventilation. Then the
gutters and downspouts go on last. If you are leaning in this
direction, you need a construction company that will consider the whole
system for you rather than a "shingler" that only applies roofing
material.