I saw your post and as I have same cpu and mobo but I'm getting 4.3GHz all cores solid as a rock I'm a bit surprised with the cooler you have that it's not stable and getting better results for you.
My rig is this...
2700X @ 4.3GHz (25-28 deg idle and never seen higher than 52-54 max load after 3 hours in FH3 or FM7 @ 6048 x 1080) But I am in Scotland where it's currently 18 degrees max during the day just now.
16GB HyperX 3333MHz (not on QVL list as yet sadly so running at default of 2400 CAN get 2800 or even 2933 but it's unstable atm)
X470 PRO (ver 4011)
RX Vega 64 with EK-WB Vega block 7% core clock boost (1742MHz) 1050MHz HBM2 +50% power never above 50 degrees yet.
XSPC Raystorm Pro D5 Photon RX 360 watercooling Kit (Intel+AMD) This is most likely the reason for my stability @ 4.3GHz as the rad is 48mm thick.
Samsung 960 EVO 256GB NVME M.2 SSD
Seagate 3TB HDD
OCZ.1250W Gold series PSU
Win 10 Pro ver1803 fresh install when I got the CPU and MOBO on launch.
I also noticed the stock fan setting would ramp up and down on BIOS 4011 so again used the fan options in the BIOS and just set them to max (no where near as loud as a reference blower)
In the past I had used Asus AI Suite 3 to OC the system but after seeing voltages of 1.55V I manually edited that down to a max of 1.475V as temps were a bit high for my taste, SMT is on, but I have since disabled the boost function as the CPU had tried to run @ 4.4GHz when I'd set it to 4.3GHz whilst that did give a result in Firestrike it crashed in games far too often AMD Radeon RX Vega 64 video card benchmark result - AMD Ryzen 7 2700X,ASUSTeK COMPUTER INC. PRIME X4...
Max core speed of 4.368 when reported max shows 4.4??? never tried it higher than 4.3 manually so why did it try and run @ 4.4?
This is what I got after disabling the core boost function in the BIOS
4.3 Max core speed 4.303 actual and stable 24/7
Ran Cinebench just to check the scores I'd get for comparison
OpenGL 113.98fps
CPU 1909 cb
CPU single 178 cb
What's interesting is that the CB single core is within margin of error your 4.26 boost vs my 4.3 allcore OC result just 1 point in it...
Having said that even with the wraith stock cooler I was hitting 4.1GHz all cores and it did hit 4.35 turbo on a single core....
One other query? What case have you got?
Main reason I ask is that in my past experience I've had far better case temps and CPU temps (HAF X but now using a Thermaltake Core X5) using a reference GPU with a blower cooler as it exhausts the hot air OUT of the case and not into it. That was what I saw with My old R9 290X Sapphire 8GB card I had vs a 390 8GB reference blower cooled GPU. I got far less CPU throttling with the blower than the AIB cooler....
Reducing the ambient temps inside the case.... it's a minimal difference but could be crucial if it's throttling due to temps but having seen review OC's of 4.3 GHz and temps topping out around 90 degrees before hard throttling I think you may just have lost the Silicon Lottery...
Possibly a "bad core" affecting the multicore clocks? I don't really know enough tbh.
Think your best bet is look at watercooling even a 240 x 120mm AIO SHOULD give you more headroom again as it removes CPU heat right out of the case plus it's not going to be affected by heat rising from the GPU backplate soaking into your CPU coolers fin stack, especially for all cores overclocking and like I said disable XFR2 in the BIOS as it might be trying to boost on top of your selected overclock when you're not looking.
even trying the GPU in a lower slot on the Mobo could have a beneficial effect as that would most likely be your systems biggest bottleneck atm.
Hope you get something useful outta my ramble there anyway dude.... If you wanna know what my BIOS settings are gimme a shout and I'll check them in detail... Never know could help out 
EDIT: check the BIOS TPU settings as I'm pretty sure "Auto" is for the wraith cooler "TPU 1" is for aftermarket aircooling/AIO options and TPU 2 is for watercooling. this seems to affect the max boost speed achievable if XFR is enabled... just remembered that I had to set it to TPU 2 myself....
Sorry to hear that,but i think i lost the Lottery too.I can not say is Amds fault because Only the base is guaranteed and bosst and overclocking is a luck thing nothing else..
Maybe next time better luck... 
