Every HP 6300, 8300 Small Form Factor, the most popular choice, has graphics card length and height restrictions. The HP 6300 MT also has a max graphics card length of under 7 inches due to the motherboard layout/heatsink placement. The 8300 MT can use cards that are full height and longer than 7 inches but that don't require 6 pin supplemental power. The main objective of these HP CustoMacs is economy, to save money on the cost of the build and to reduce electricity usage to further save money over the usable life of the machine. The single fan 1050 Ti should perform as well as the dual fan version, it might run slightly warmer under heavy usage. You can use the longer dual fan version in the 8300 MT if you need extra cooling.
If you are editing in Final Cut professionally you should be using a CustoMac built from the ground up with new compatible parts. That gives you a wider choice of power supplies and graphics cards. The HP 8300 is pre-built with a proprietary PSU that should not be replaced.....