How to customize Prefix Delegation?

Installing and Using OpenWrt Network and Wireless Configuration
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I'm tortured this do , now I test as work only IPv4 and I see but wht I stuped when try use GoodBye DPI , I'm use this so stuped , what to I'm help ISP do DPI not passable. Now I meen my stup.
But I not understand , why if I use IPv4 only speed more stable , how I use IPv4 and IPv6. Speeds range if I use only IPv4 in megabits 188-199 megabits , Speed range if I use both connection 122-188 megabits , why so ? Ping also with both connection baded 7 - 30 ms with both connect , and 3-7 ms if use only IPv4. Why so ?