An imperial stout has high alchohol. To get there the starting gravity is usually much higher and to balance the fermentable malt , more specialty grains are used (unfermentables) so the finishing gravity is also higher. that all means a stout has more alc and is more full bodied.
Although stouts and porters names have been used interchangeably for a long time , today most people distinguish a stout from a porter by the presence of roasted barley which has a very distinct flavor. Souts have roasted barley , porters not by todays style descriptions.
$15 for a 4 pack would keep me away too!
