The R8500 would be much slower than the R7800 which should hit ~80-100 Mbps on aes-128 as mentioned by some including Kong on the DD-WRT forums. Haven’t used stock much to comment as I mostlly am using a newer gen Netgear test firmware or OpenWRT. The 86U would definitely be faster as Broadcom finally implemented crypto acceleration and might actually be a better pick, the only thing the R7800 has over that is the WiFi performance and not by much.
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