The beer would be dark, sweet and sour and Porters have generally evolved to be kinda sweetish, but the sour component has been phased out for commercial reasons.

Stout evolved from the most alcoholic combinations of Porter, originally being known as Stout (ie  strong) porter. In order to substitute for that fat alcoholic flavour (originally 7 - 9%) the hop rate is very high, resulting in a bitter flavour, a very different beastie from the sweeter porter.

Many craft breweries around the US do an Imperial Stout, I have one at home here to try. In Chicago, Rock Bottom seem to brew an Imperial Stout as do BJ's. Google Chicago and Imperial stout. Without having tried Baltika, I have a lot of respect for American craft brewers and doubt you'll be disappointed.

keep to the Fen Causeway