You know the funny thing about the Ian Hill model is that it's really a typical Kramer-Era neck. Because the guitars made in Brooklyn and at Kramer didn't have the Carbon Fiber supports, the necks could be thinner front to back.
The thing about the Ian Hill (and I've played several, there's always one available at NAMM at the Spector booth to demo) is that for those of us with NS-2A basses, the neck is perhaps a mm or two at most thinner than the typical NS-2A neck.
That's what the measurements I've taken show. The most important thing to take away from this is that of all of the guitars I have, the NS-2, NS-4, Euro4LX, Euro5LX (we can't include the B.O.B. bass in this because as a bolt-on it's got a much thinner neck profile than the NT models)...
Of those basses mentioned above, my NS-2A has the thinnest front-to-back neck thickness/profile. So shave another one or two millimeters off of it and you have the Ian Hill models.
Even my Alex Webster, which has a thinner neck than they typical Euro5LX, has a thinner front to back profile than The Black Pearl.
To be honest I don't really notice the thickness of this or that neck... the bigger variable for me has been when I move to a bass with the 1.5" nut and string spacing.
To this day I still say my favorite neck profile to date has been the one found on the NS-2JA-R. I love, love, love the necks on those basses. And they have a 1.56" nut.
I played a Euro4LX Doug Wimbish at NAMM and really thought the neck felt great. So I'm excited to have ordered a USA NS-2 Doug Wimbish Signature Model today. PJ put the order in today.

It looks to be a cool/unique as The Black Pearl. So I'm really stoked about that. More to come as it is being built.