The issue some are having with your post is that you are comparing a few cabs with different driver sizes, and then assuming it is the driver size that is causing what you are hearing. In fact, it is more about the voicing of the cab and quality of the drivers that is driving what you heard.
To the OP, besides woodshedding your chops (you know you have gotten there when you can pretty much play everthing you can play fingerstyle using your thumb, at the same volume), the key to a good slap tone live is to have a rig that is full range and that won't compress when you hit it with those peaks. Most of the great slappers I know don't use a compressor, but that can help a bit. However, you should NOT start using a compressor until you have your dynamics under control without one.
So, you need a bit of power, and a cab with a GOOD quality tweeter or mid driver, and woofers that have decent mechanical spec's. Most high quality 212 or 410's will get you there IMO and IME. Most two way cabs with traditional tweeters have a pretty nice voicing for slap, since that 'gank' area in the 1K region usually has a built in 'dip' in those designs. So you get all the bass and mid mids needed, but have a nice airy, non clacky top end. Don't confuse this with those 'enhance type' controls, which typicall scoop the 'wrong' mids for a good tone live.
That probably isn't much help. It is all about the mix and match of bass, technique, amplification power and voicing, and especially speaker mechanical specs (i.e., the ability of a driver to handle a nice transient without compressing, and a tweeter or mid driver that is sweet and not harsh).
IMO.
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