modem/router combos = nope.avi
they are HORRIBLE. not only is the wifi horrible, the router has absolutely no settings at all and the modem is also generally garbage.
replace everything.
buy a new modem (look for something like motorola SB6121 or SB6141), then buy a separate router.
You dont need wireless AC unless you are paying for a 1Gbps connection from your ISP. wireless N can support up to 600Mbps connections. i have the best connection available in my area and its only 300Mbps, so its not likely you have above 600+Mbps from your isp. if you do then get an ac router.
of any consumer router, asus routers imo are the best. i have a ASUS RT-N66U and it works great. (routers with external antenna generally will give you better wireless performance)
But know ping is based generally on distance and packet loss (packet loss is caused from poor wireless signal or wireless interference). what ever you get using a direct connection is about the best you can expect. so even with good wifi with no packet loss, it wont ever out perform wired.
Its possible (especially with others using your network), that your modem doesnt have enough download/upload ports, and is causing traffic leaving your house to be congested (meaning a new modem can help lower your ping). so it is possible a better modem and router can lower your ping below your current wired right now. (it should definitly help with extremely high wifi ping)
So assuming youre modem and router are not impacting your ping in any way, then there is not much more you can do. higher ping is caused by the distance form you, to your ISP to the server.
data has to go from your house to your isp's servers. from there it travels to the game server. then back. that is what ping is, the time it takes to get there.
But sometimes your isp will not take the best route to get from them to the game servers. in america especially where the internet infrastructure is ****, this is a common occurrence. if you have crappy isp like comcast, time warner, or verizon, you may want to look into a gaming VPN like WTfast or pingzapper to lower your ping (in a normal sense, a vpn will always increase your ping and lower your speeds, since you are making an extra stop on the journey to the server. but in cases where isp's are being **** with routing your data, it can lower ping and increase speeds).