Alexander's pale is 100% North American 2-row Klages malt. Briess Gold and Pilsen Light are mashed with North American 2-row and Pils malts respectively, though each contain a proportion of CaraPils. Briess's Organic Light extracts are mashed with 100% organic North American 2-row. Cooper's I know nothing about. Muntons does not list ingredients.
Anyway, just because you can't do a full five-gallon boil doesn't mean you can't do all-grain. There's no law says you have to do five-gallons or larger batches! I'm a stovetop brewer, too; I just do 3-gallon batches. Yeah, it's less beer in the package, but I justify it like this: I get to brew more often, have more varieties in the bottle, and play around more. I'd never do 5 gallons of mocha porter, but 3 gallons? Maybe.
In fact, the SMaSH in my sig - of which I've only got something like three bottles left - was all-grain on the stovetop. 3-gallon batch, and yummy as the day is long.
You want my opinion, if you want to do a SMaSH partial mash, go organic. Get some Briess organic 2-row and mash that. Bring it up to 5 gallons with some Briess Organic light extract. From all the information I can find, it's the exact same malt. Get yourself some organic hops, bottle-condition with organic cane sugar, and be all hippy! I think I might go organic for my next batch. Dunno.