From experience, larger diameter hoses and wands, on the order of 38-40 mm diameter, maximize airflow. Some modern Japanese canister vacuums use hoses as large as 48 mm inside diameter! Modern Hitachi hoses are 48 mm at the canister end and 46 mm at the hose handle. Also, gentle curves on hose ends and swivels, help airflow. Sharp bends like those old pistol grip handles that Electrolux and Tristar used are death to airflow. Keep the airflow through the vacuum as close to linear as possible. Hoses that attach to the front of the vacuum instead of a top mounted swivel flow better. Also those top mounted swivels often cause the vacuum to tip over when the hose is 90 degrees to the body. An expander cage to keep the bag off the sides of the bag chamber helps maintain maximum airflow as the bag fills up. Look at a Hitachi Karupack canister and the Panasonic MC-PA20, MC-PA21 and MC-PA22 canister vacuums, all of these are Japanese market canisters, for what a vacuum with high airflow looks like and the Panasonics have the kind of expander cage I am talking about. Scale these up a bit for a longer cord, longer cord and a bit more bag chamber capacity and you would have a winner I think.
