It depends on what it's primary use is. If it's just for viewing content and internet surfing VA is perfect for that. If it's for photo or video editing then IPS is the best choice. Ultimately when deciding you have to look at the monitor in person to give it the eye test to decide if you'll like it. You've always got a 30 day return window so try it out and see if it works for you.
AFAIK you don't want to to use KernelXCPM in a Haswell system. Only with Ivy Bridge. Using generate C and P states should be OK. I'll have to look into this some more later this weekend. Not sure why idling doesn't reach 800 MHz. What is the amount of power your CPU is using ? You might also check the power mgt. settings in BIOS to see if any changes there might affect CPU PM.
Make sure to avoid the super cheap adapters shipped from China. Many just don't work. They may be wired wrong or use very low quality components that could fry your motherboard. It's worth spending a little more to go with the moddiy version of this adapter.
Have never owned one of those. Once you are getting close to 450-500 pounds in cost it's probably better to build a new 6 core i5 system that is coffee lake based. That being said if you really want a Dell it should be workable. If you look at the performance comparison between the i7-4790 and i7-6700 you only gain a little better single core performance, that's it.
I love your 6300 build; it is so easy,cheap and stable. It is more than enough for me. Although lack of NVIDIA drivers for Mojave forced me downgrade GPU, it is still good. Now editing videos for my new business makes me want to buy a new computer that can handle FCPX more smoothly. I can brings part together and build one, but I am not so sure how complicated it will be. Spending more time in the beginning is not an issue, but I dont know how stable it will get. I just thought whether Dell 7040 could be an options simply because I assumed it will be similar one to 7020/9020. I have no clue about Dell or other systems, but I'm merely following/adapting your advice which I appreciate greatly.
