If 950MHz VRAM is perfectly stable, you're right to not push it further. There won't be a huge FPS difference.
A brick can occur so easily/abruptly nearing 1000MHz...
About the sound issue, this is the first time I've heard of these kinds of problems.
Are you sure it's not the fault of these config files ?
To anyone reading this :
For testing purposes, use the previous Beta 8 .PUP.
https://app.mediafire.com/0uxvp5ismnjwm
If the file you're searching isn't already made, then ask me.
Once you've found your limits, feel free to ask an updated version.
750/900 EVILNAT 4.91 BETA 9 PEX
https://www.mediafire.com/file/qsxlvsf286vur6c/750_900_BETA9_PEX.PUP_4.91.CEX-PS3UPDAT.zip/file
I also remind you that
this tutorial exists

(If you really can't make it work, then it's ok. There are many compatibility issues it seems, so ask me.)
Another reminder for our new testers :
Please dump your LV1 (in Evilnat options, search for the "Extract" category), search this kind of string and share it here.
Code:
rsx65 a06 650/900 vpe:ff shd:3f [K4A049400:1:2:16:c:c:3:8:2] [1c:0:2:0:1:2:0] [2:1:0]
It's easy, just search for your RSX speeds with any Hex editor and you will find it. In some HEX programs, you'll need to do a "back search" for it.
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