I'm probably ages too late to reply to this thread, but I will anyway.
I have mixed feelings about the B5E, which I've had for about a year now. At first, I was stoked about having my first 5-string, all the great features, etc.; and I was especially interested in learning to slap. Well, long story short, I did learn to slap on the B5E and was none the wiser until I picked up a mid-90's used Peavey Foundation 5-string from craigslist for $200. The Peavey, despite its age and being half the cost, puts the B5E to shame, slapability-wise. It reminds me of the MIA Fender Jazz' and Musicmans I play with at GC. I now kinda wished I wouldn't have gotten the B5E and would have just waited until the Foundation came up for sale, but hindsight is 20/20.
I'm no expert on the matter, but now my impression is that bolt-on necks make for better "slappers," and that, on average, MIA bolt-ons will take the competition in this category.