Detailed Answer
Gutter sizing is determined by roof drainage area and rainfall intensity, not total square footage alone. The 2,000 sq ft figure refers to living space, but the relevant number is the roof's projected horizontal area — which can differ significantly depending on roof pitch and configuration.
For a standard 2,000 sq ft home with a moderate roof pitch (4:12 to 6:12), 5-inch K-style gutters are the correct standard choice. They handle the drainage load from Sacramento's typical rainfall events and are the most common size installed in Sacramento metro. Paired with standard 2x3-inch downspouts at appropriate spacing (one downspout per 40 feet of gutter or less), a 5-inch system performs well for most properties.
Upgrade factors that warrant 6-inch gutters: steep roof pitch (8:12 or greater), which concentrates runoff faster at the eave; large uninterrupted roof planes that funnel water into a single gutter section; heavy tree coverage that requires gutters to drain fast before debris causes localized backup; or homes in neighborhoods that get concentrated storm runoff. New construction in El Dorado Hills, Folsom, and parts of Granite Bay often features 6-inch gutters as standard due to these factors.
Downspout sizing matters as much as gutter width. 3x4-inch downspouts handle significantly more flow than 2x3-inch and should be used wherever a long gutter run feeds a single outlet, or where the roof pitch is steep. Upgrading downspouts on an existing 5-inch system is often a cost-effective improvement that prevents overflow without full gutter replacement.
For new installations, 6-inch gutters cost only marginally more than 5-inch but provide meaningful surge capacity during atmospheric river events. If you're replacing gutters on a home with significant tree canopy, the 6-inch option is worth the marginal upcharge.