Check the Premiere Pro specs and Hardware List for surety.
Stick with an Nvidia chipset, such as GeForce GTX 760, 770, or 780 for instance.
For the PC in general, avoid AMD processors, go with Intel Core i7, 16GB RAM or more, SSD boot, dedicated fast drive for VIDEO content, robust power supply etc.
Safe Harbor Computers
For the CPU, might want to look at the new Haswell 3 I think it is. Not sure how spendy, but a lot of the motherboards for H-3 chips are designed with 8-10 SATA-III disc connections right on the mobo ... makes building either many single-disc or a couple RAID arrays using the motherboard resources quite a snap. But as it's just coming out, might be a bit pricey ...
Buy a Desktop Video Editing PC
Here Build a Desktop Video Editing PC
-3 price level ideas in http://www.pacifier.com/~jtsmith/ADOBE.HTM
-what PC to build http://forums.adobe.com/thread/947698
-2 how to build videos http://forums.adobe.com/thread/1104182
-another video http://forums.adobe.com/thread/1145366
-another video http://forums.adobe.com/thread/1132363
-planning & Building http://ppbm7.com/index.php/intro-part-1
-memory for LGA2011 http://forums.adobe.com/thread/1098759
-an Adobe FAQ http://forums.adobe.com/thread/878520
-several more links http://forums.adobe.com/thread/815798
-build tuning http://ppbm7.com/index.php/final-results
Neil, I think you mean Haswell-E with the new X99 motherboards and DDR4 memory.
Yeah, that's it. See, this is why I have my builder actually do the work with this stuff ... but darn if you and a couple others aren't an amazing resource for pointing him at ...