Hydra453

as far as some chips go it definatly can help you squeeze out quite a good extra bit of mhz or let you run MUCH cooler. But that also depends on how good of a silicon lottery you got with your chip so there is always a risk it may do very little for you in the long run besides thermals. Also there comes maintenance where it will degrade much faster so those results you saw 6mo ago or a year ago may be gone in that much time without reapplying. Which again can be easy or super F'n difficult if say you are full custom loop and even worse for the situation using hardline. But say you have a 7700k and $80 or more to blow on a delidder and liquid metal unless you find a good deal are you willing to do that for possibly no gain? If yes go for it if no than its not something to consider its advantages on at all. It is an ENTHUSIAST market item not to be treated as a necessary part of a complete build unless you like OTT stuff.
That being said it is something i would do on again a 7700k and maybe a few other cpu im not sure there are much reports on stellar improvements on a 9700k i would assume it would not cool as more just due to the magnitude of cores pushing out heat so rapidly so you may end up with 50% the gain at best of other more traditionally delidded cpu.

It's not worth the effort to delid a 9700k, clean off the solder and apply liquid metal for a ~10°C gain. That is without taking the possibility of breaking the die into account.
 
With Coffee Lake, when the odds of damage was close to zero if you used a proper delidding tool, and the gains were 20°C, a good argument could be made for delidding. However, that is not the case with 9th gen.

Gumtree.

Use gumtree, ebay or craigslist

with how much the i7s cost used, he could have gotten the 1600 and a decent B350 board at a similar price, which would have done better.

Chief, the 1600 came out ahead of the 7700K, by almost 2 minutes.
The 1700X also came out ahead by quite a bit.

Oh yes and I suppose DDR4 makes no difference as well.
OP asked if the i7 7700 is a worth investment over the i5 6400, short answer is that it is, and it'll be much cheaper specially with second hand deals poping up than migrate to a new platform... that's all.

Do you even have or have used Sony Vegas? it is a 4c/8t optimized software having in mind old standard for the i7's throwing more cores at it just like with Adobe Photoshop and other 4c/8t optimized applications scales rather poorly, the best is faster cores before more cores by every mean meaning the i7 7700 is a much superior alternative than the Ryzen 5 1600.
 
OP Your experience will be a lot superior with the i7 7700 and you'll get to keep your platform reducing costs, if you can go for it go for it, even with the current 6 cores mainstream the 7700 is no slug and should be meaningful until you can do a bigger upgrade with 10nm upcoming processors in the future when the software will then finally take all the proper use from it.
 
Something like a Ryzen 2700x would only make more meaningful sense if you multi-task a lot with other many side programs running at the same time as Sony Vegas.
 
As we can see it is not unusual to people believe raw core count is all that matters for rendering but the truth is the single thread performance is as important, Ryzen is not the answer to all workstation necessities: the 4cores holds strong against the 8 cores ones:

It is a shame you can't get the i7 8700 boy this one is a dream on Sony Vegas Pro, I use it myself :3
 
 

Only depends on the workload, really. If you upgraded a much older GPU, you still got an improvement. And if you're playing something in the Esports category, the CPU shouldn't be a bottleneck.
 
Given the fact even the Ebay route seems to be about $250 USD for a 6700k & you already have DDR4 memory, it's really just about how much do you want to spend?
 
If staying Intel, you could grab a B360 Mobo for $85 & i5-8400 for $180, so around ~270 with shipping.
On the AMD side, you'd probably want a X470 board with a Ryzen 5 2600X. So that's probably ~120 + ~220 for around ~340. 
 
Though I think either of those could hit something of a snag with your Memory. You'd probably have to spend a chunk of time OC'ing the memory and getting good timings, on both platforms. If you want to "build for the future" a bit, get a Z370 board and the 8400. A little more, but you get full OC options for the Memory and could upgrade to a 8700k in the future. Or just go all-in and grab the 8700k now.

He doesn't have a Z270 board, in addition it's not worth spending any money on kaby lake, for close the same price you could just get an R5 1600 + ASrock Pro 4
 
PCPartPicker part list: https://pcpartpicker.com/list/NVwy7h
Price breakdown by merchant: https://pcpartpicker.com/list/NVwy7h/by_merchant/
CPU: AMD - Ryzen 5 1600 3.2GHz 6-Core Processor  ($174.88 @ OutletPC)
Motherboard: ASRock - AB350M Pro4 Micro ATX AM4 Motherboard  ($74.39 @ OutletPC)
Total: $249.27
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-04-19 00:28 EDT-0400

I have a 1080 myself and if you have a high refresh rate monitor and play some demanding titles then I'd definitely go with the ti.