I like your spreadsheet
Unless you don't care on spending an additional 1000$, the I7 4790k is definitely in a better spot. Sure, the extra performance is going to be considerable, but then you should just go with the 5930k or better yet the 8 core 5960x. As for gaming, the 4790k will probably outperform the 5xx0k/x, due to it's higher clock rate. For rendering, the haswell-e's will outperform the devils canyon.
PCPartPicker part list /
Price breakdown by merchant
CPU: Intel Core i7-4790K 4.0GHz Quad-Core Processor (£243.99 @ Ebuyer)
Motherboard: Asus MAXIMUS VII GENE Micro ATX LGA1150 Motherboard (£142.98 @ Aria PC)
Memory: G.Skill Ripjaws X Series 16GB (2 x 8GB) DDR3-1600 Memory (£108.35 @ CCL Computers)
Storage: Samsung 840 EVO 250GB 2.5" Solid State Drive (£89.72 @ CCL Computers)
Storage: Samsung 840 EVO 250GB 2.5" Solid State Drive (£89.72 @ CCL Computers)
Storage: Western Digital BLACK SERIES 1TB 3.5" 7200RPM Internal Hard Drive (£55.00 @ Amazon UK)
Video Card: Zotac GeForce GTX 980 4GB Video Card (£409.98 @ Ebuyer)
Case: NZXT Switch 810 (White) ATX Full Tower Case (£130.57 @ Scan.co.uk)
Power Supply: SeaSonic X Series 850W 80+ Gold Certified Fully-Modular ATX Power Supply (£140.65 @ CCL Computers)
Optical Drive: Samsung SH-224DB/BEBE DVD/CD Writer (£10.46 @ Aria PC)
Operating System: Microsoft Windows 8.1 (OEM) (64-bit) (£72.35 @ Aria PC)
Total: £1493.77
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2014-11-09 15:31 GMT+0000
Personally I believe I brought you in under budget with what I'd consider to be the better set-up per price/performance for gaming. Now, granted you may have other ideas in mind for what you'd use your processor for, aside from gaming.
It may be better just to go with the 4790K, There will be advantages just from the DDR4 alone if you go with the i7 5820k. One thing to note about the i7 5820k is that the PCI-E bandwidth is not as great as the other Haswell-E Processors. so 28 lanes opposed to the usual 40 fro previous gen Socket-R SKUs. Also when you get the i7 5820k that is the lowest binned processor in the Haswell-E 2011-3. opposed to the highest Binned lga 1150 i7 4790k. I would opt for the i7 5930K if your going to get the X99 platfrom. Everything is going to cost so much anyway, so get the best you can.