The reason stock runs better... Well... Sometimes runs better... Is because the kernel is being developed by people with more inside access than any custom ROM dev could ever have (with the exception of that whole Oppo+CM thing...), and they're getting paid to work 8 hours a day to develop it well. Since the ROM devs don't have access to the inside kernel data, they basically have to make a graceful hack. Which sometimes doesn't work well. FWIW, I have perfectly fine WiFi access on custom ROMs, not enough of a difference to notice.
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