High vs Mid Tier Gaming Rig? (Also should I save anything from previous build)

ya you could definitely use a new build. I realistically don't see a 4790/6700k lasting drastically longer than the much less expensive 4460/6500 build.

I think that with a good bang for the buck gfx card that you upgrade in ~24mo with another bang for the buck gfx card yields good results. Or at least it has for the last 8 or so years. Keep the processor a bit longer

It's not going to affect fps, just use a bit more idle power, I used to run 3 displays off an APU

You probably don't need a sound card or a DAC at most new headphones

PCPartPicker part list: http://pcpartpicker.com/p/6tGL8d
Price breakdown by merchant: http://pcpartpicker.com/p/6tGL8d/by_merchant/

CPU: Intel Core i5-4460 3.2GHz Quad-Core Processor ($174.88 @ OutletPC)
Motherboard: Asus H81M-D PLUS Micro ATX LGA1150 Motherboard ($59.99 @ SuperBiiz)
Memory: Crucial 8GB (1 x 8GB) DDR3-1600 Memory ($34.99 @ SuperBiiz)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($49.98 @ OutletPC)
Video Card: Sapphire Radeon R9 380 4GB NITRO Dual-X OC Video Card ($193.98 @ Newegg)
Case: Fractal Design Core 1000 USB 3.0 MicroATX Mid Tower Case ($34.99 @ Directron)
Power Supply: EVGA 600B 600W 80+ Bronze Certified ATX Power Supply ($50.99 @ SuperBiiz)
Total: $599.80
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-12-10 00:51 EST-0500
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That'd be the monitor to get, 144hz, but only TN

https://pcpartpicker.com/part/aoc-monitor-g2460pf

I'd probably step the budget up a bit so you can enjoy SSDs and go with a current gen skylake for a bit more longevity.

Personally I really like having a windows SSD, a games SSD, and a storage/games hard drive.

SSDs are seriously amazing they make using windows enjoyable lol

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-6400 2.7GHz Quad-Core Processor ($178.99 @ NCIX US)
CPU Cooler: Arctic Cooling Alpine 11 Pro Rev. 2 36.7 CFM Fluid Dynamic Bearing CPU Cooler ($11.99 @ SuperBiiz)
Motherboard: Gigabyte GA-B150M-D3H Micro ATX LGA1151 Motherboard ($78.99 @ NCIX US)
Memory: Crucial 8GB (2 x 4GB) DDR4-2133 Memory ($43.49 @ Newegg)
Storage: Zotac Premium Edition 240GB 2.5" Solid State Drive ($64.99 @ Amazon)
Storage: Zotac Premium Edition 240GB 2.5" Solid State Drive ($64.99 @ Amazon)
Storage: Hitachi Deskstar 1TB 3.5" 7200RPM Internal Hard Drive ($49.90 @ Amazon)
Video Card: Sapphire Radeon R9 380 4GB NITRO Dual-X OC Video Card ($193.98 @ Newegg)
Case: Fractal Design Core 1000 USB 3.0 MicroATX Mid Tower Case ($34.99 @ Directron)
Power Supply: EVGA 600B 600W 80+ Bronze Certified ATX Power Supply ($50.99 @ SuperBiiz)
Total: $773.30
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-12-10 02:19 EST-0500