I used to have an Alnico IV SM in the neck of a Les Paul which I really liked, but it was definitely cleaner and clearer sounding than Slash's tone. A bit more like a Strat neck pickup if that makes sense?
The 'looser' bass of a regular Alnico II set of Stormy Mondays will give a warmer, fatter sound due to the slightly lesser note definition the weaker magnet gives. They rock out as Ilyti says, but you won't get that super tight chugga-chugga-chugga. Doesn't sound like that's what you're after though!
I play guitars with very similar pickups (no SMs, sorry Tim!) but I go from AC/DC to Whitesnake to Judas Priest to Airbourne etc using vintage Marshall clones and a couple of pedals. If your using gain levels from clean up to "old Marshall with a Tubescreamer" they'll be great. However, I don't think they'd be best suited to death metal on a Mesa Dual Rectum Fryer........