@grrr2 thanks for all the points, and yes I read this thread and understand a bit how crazy I am to try to use 4Gbps. actually, I don't have real demand on my home servers for 4Gbps yet. I would say 1Gbps is even good enough for now. for me 2.5Gbps would be a good compromise also in terms of money for hardware and future-proof.
for router, I am really thinking of building some custom home router with more memory mostly to try out deep packet inspection and study a bit of enterprise networking features.
but I am mostly worried about having the best possible AP that OpenWRT supports in terms of performance, since I know the focus of OpenWRT is more on long life support for older hardware and that means mostly not supporting latest shiny APs on the market. than I would like to invest here to get the shiniest, with best performance to be more future proof (I rely a lot also on wifi speed since some of my devices that needs speed are difficult to reach by cable), and also because of my bad experience with Linksys WRT3200ACM.