Most info I got from
www.tonymacx86.com . Dont get an Nvidia card for FCPX, ATI Radeon work MUCH better. Use Nvidia for Adobe products, such as Premiere.
Here is the machine I recently put together:
Crucial Ballistix Sport XT 32GB Kit (8GBx4) DDR3 1600 MT/s (PC3-12800) UDIMM Memory BLS4K8G3D169DS3/ BLS4C8G3D169DS3
Amazon link
Intel Core BX80646I74790K i7-4790K Processor (8M Cache, up to 4.40 GHz)
Amazon link
Gigabyte GA-Z97X-UD5H LGA 1150 Z97 with Killer E2200 and Intel Gaming Networking SATA Express M.2 SSD ATX Motherboard
Amazon link
Seagate 2TB Desktop HDD SATA 6Gb/s 64MB Cache 3.5-Inch Internal Bare Drive (ST2000DM001)
Amazon link
Samsung 850 EVO 250GB 2.5-Inch SATA III Internal SSD (MZ-75E250B/AM)
Amazon link
Corsair Hydro Series H110 280 mm High Performance Liquid CPU Cooler
Amazon link
NZXT H440 Mid Tower Case (White)
Amazon link
Sapphire Radeon VAPOR-X R9 280X 3GB GDDR5 DVI-I/DVI-D/HDMI/DP TRI-X OC PCI-Express Graphics Card with Boost (UEFI) 11221-12-40G
Amazon link
CORSAIR RM750i High Performance Power Supply ATX12V / EPS12V 750 Power Supply CP-9020082-NA
Amazon link