as much as I noticed from working with GIS data I noticed that CPU speed seems not to be the limiting factor (I have a AMD Phenom II X6), but the I/O performance of the disks (currently WD Blue) as well as working memory (i have 16 GB). What I'm doing mostly is importing OSM-data to a PostgreSQL database and use this data for simulation purposes. The importing takes me about 2h and I run out of memory on 2/3 of the way and linux starts using the swap, which slows down every thing.
Taking into account what you wrote will be your main uses of the PC it is important, that you are able to have lots of RAM starting from 32GB, which is the limit of current Haswell. I do not know about AMD, but what I found quick was 64GB. Anyway I would recommend you to go towards Server CPUs like the Intel XEON, since they support ECC-Ram which will be really useful on long memory intense calculations. Worth mentioning are also the new Haswell-E.
Otherwise I would recommend you SSD drives, especially if you use databases like PostgreSQL. If you want to go all out for PCI-E SSDs.
In the end it will depend on your budget, but the most important points for you I see are RAM and I/O Performance.