For those planning a V-belt drive you can get it right the first time if you study the Reliance/Dodge enginering catalog. Dont let the thick stuff in the first couple pages deter you. On back you will fing easy to digest info on things like how much HP per belt with a given diameter pulley, belt length, ratios etc for each stock part they sell. Link provided is for classic A-B belt drives. Other sections will give same info for the "L" series belts and the "V" series that are not so common outside of industry.
The link http://www.dodge-pt.com/pdf/catalog/pt_components/2004_pdf/vdrive_stock_drive_sel.pdf