Iain - I could not find the data I was looking for so I went in search for you and happened upon some of the information I had stored previously. Like Jac - I've made great reference out of Circle Track Magazine - I used to love reading Smokey Yunick's column.. Speaking of Smokey, as I recall his adiabatic engine used reverse flow cooling and a custom (wasn't everything) water pump of his own design.
Here's a good informative article on Evans NPG which addresses the design of the impeller not to a great depth, but some..
Circle Track - August 1997 Centrifugal pump design - step 3 for beginners
The key thing to control in a high RPM design and implementation is cavitation. The more turbulence you have in the pump housing (volute) the greater the opportunity. Of course yet another key is the design and execution of the impeller blades.
I'll still continue my search for my own files as I am really curious what became of them as we had done some experimentation with pumps for high RPM SBC applications that worked out quite well at the time on engines that turned from 4000 to 9500 RPM.