im assuming u are upgrading to stiffer springs
but to answer ur question shortening the stroke is the same as shortening the travel in the piston or shock
is your car same height as it is in your members ride?
it will allow you to go lower but that depends if they shorten the shock body also
has your car ever bottomed out ? like your upper control arms?
if you are slammed your going to bottom out no matter how good your setup is. but doing that to your shocks will help a little bit, also, your spring rate plays into it as well.. if you shorten the shocks, your gonna need stiffer springs.