Supercharging id run no bigger than a "R" cam. Too big a cam and you will bleed boost off due to too much overlap.

WIth a K20 id look into the Rotrex aka Kraftwerks superchargers, they are really nice and make as much power as a turbo.

Benefits to supercharging (JRSC) is its cheap, good power, easy to install , no bov, no wg, no turbo manifold, no turbo etc

Cons it only makes SO much power, it gets hot (no way to use an intercooler)