> Compare performance of a typical pice of high-end hardware in IPv4 mode and IPv6 mode: "128K routes for IPv4" vs "64K routes for IPv6", "up to 60 Mpps of IPv4 packets" vs "up to 30 Mpps of IPv6 packets", etc.
At least some of that could balance out in the end, as IPv6 should require fewer distinct routes and allow more data to be included in each packet. (IPv6 raises the minimum MTU from 576 bytes to 1280 bytes, and the maximum packet size, without optional extensions, from 1500 bytes to 64KB. With options the limits increase to 64KB for IPv4 and 1MB for IPv6.)