What is under $5k speaker with best bass slam?

I do not claim to be an expert in these matters, but dude....I tried my best to replace my kef 107's, but at the end of the day I just couldn't do it. Those two 10inch woofers gives me that DEEP bass that I love. I looked at revel salons and b&w N801 and decided to stay with my kef's. At least until I can find those at the absolute right price. Try to get your hands on a pair...you won't regret it!!

Von Schweikert speakers

That's easy, get a pair of original Energy 22 Reference Connoisseurs....they easily go down to 25hz and more like 20 without breaking a sweat.

Will 12" drivers produce slam in a 12 by 12 room?

In a room that small, I'd think your biggest problem wouldn't be finding speakers w/ slam, but finding speakers that won't overload the room w/ bass so that it cancels or muddies everything out.

Room modes are going to be a bear in an untreated room of that size. Try this Room Mode Calulator to see how it looks

Nothing beats active bass speakers like Genesis VI or V & Vandersteen V.