I think it will increase your speeds. I base this on the facthttps://smile.amazon.com/ that I had an R7000 and the R7800 WLAN coverage is much better. I noticed increased speeds on my devices going to the R7800.
Also.. I have gigabit internet service now and I the first thing I noticed is one my cheap wired gigabit switches (TPLINK) was not capable gigabit...topping out at 600 Mbit (switch connected to my R7800 with a Cat6A cable). I replaced it with a netgear switch and was able to get the wired speed up to full 950Mbit.
What I'm saying is gigabit service can really show bottlenecks in your network. Based na on talk on the ASUS and buying advise forums the RT-AX86U is really good..should help both WLAN coverage and total throughput (wired for sure) with gigabit internet service. I have read though on my ISP forum that one person was getting better throughput on his ISP fiber gateway/router than with his AX86U going trough the ISP gateway in bridge mode. I would think that would not be the case for everyone and every ISP.