According to their descriptions in SD's and DiMarzio's pages, the ones you mention are supposed to sound like an Invader / Super Distortion type humbucker, i.e. very hot and fat, lots of bass and mids, little treble. I haven't tried any of them so I can't comment how well they achieve that objective.
The one I have used and is probably my favourite pickup ever in terms of versatility, is the DiMarzio Pro Track. Very close to a vintage humbucker wired in series, very close to a single/coil but with no hum wired in parallel, splits nicely for in-between sounds. I must say I've only used in the neck position, but SD's Little '59 is supposed to be very similar (according to a friend who has tried both) and they do have a hotter bridge version.
The other one I have is the JB Jr. in the bridge position of a Squier Strat with a Walnut body. This one is more of a hot bridge humbucker but higher-middy / trebly rather than fat, in the style of the full size JB, although it doesn't quite nail its tone.
I just did some pickup swapping in a couple of strats and I have found the tone for me, I'm using a JB Jr.neck model in the bridge of my strat. This thing blows away my Custom 5! I would seriously recomend it.
And to answer your question about the difference in sound, I've read that single coil sized humbuckers will generally lack the some of the 'chugging' low sound of a full sized humbucker. I personally found that great as I love mids and tend to get annoyed at a overly loud palm mute.
I've got my Roland G-505 (the strat style G-series axe)
wired up with a Duncan Classic Strat stack in the neck, a
DiMarzio HS-3 in the middle (I love this pup in the middle!)
and a Duncan Hot Strat stack in the rear. I tried a Hot Rails
a few years ago and found it just too high output and way
too muddy (midrangey) for my liking.
In my case I was looking to keep things pretty "stratty" yet
get rid of the hum, and I've accomplished this. If you're
looking for more of a 'bucker tone, then yes, I've heard the
'lil 59 does a decent PAF and the JB, Jr. is a nice bridge pup.