router - Repeatedly high ping - caused by WiFi or provider?

I have an ISP with a 10gbit broadband connection. I can usually download with about 1.8mbytes/sec, so that's not a problem. However, I sometimes have a very high ping in online games (> 200ms). It happens sporadically and can not be reproduced, maybe every second time I want to play online.

I always make sure no other programs which require Internet access are running, but as I said, that doesn't help.

The computer I am playing with is using a NETGEAR WNDA4100 N900 Wireless Dual Band USB Adapter to connect to a NETGEAR N300 Wireless router just 5 meters away, and only separated through a thin wall. Since these two are from the same manufacturer, I reckon they shouldn't have problems communicating.

So what other reason could there be? How can I even debug this? Would upgrading my ISP speed to 25gbit help?

Your wifi, if not dropping packets (you can see this when you ping your router itself) won't add more then a few milliseconds to your connection time.

There is a difference between ping in games and ping to for example google dns (8.8.8.8).

When pinging to for example google's dns servers are deployed world wide and you'll automatically be directed to the nearest server for the best response time.
Also the servers you are pinging to have no issue handling the load because there isn't a lot of load and neither are there long concurrent connections, just a quick "hey what's the ip for this domain?"

On game servers there is a lot going on.
Some physical machines might be offering to many game sessions at one time for their own good.
Each game session these days has anywhere from 24 to 64 concurrent connections (sessions) sending a lot of data back and forth.
When the server starts to reach its limit (mostly on processing) your game client and/or the servers' session itself will have to start waiting for the next tick (full process cycle), this phenomenon is known as lag, it can be caused by either connection failures the server crumbling under pressure.

And then theres the thing that google's dns has but the game server doesn't:
They're mostly not load balanced or spread over the world.
So if you join a game, (if you can) check where it's fysical location is because the further away the higher the ping by default.

The internet speed has no effect on pings. Even the slowest of connections can have better pings. Pings depend only on one thing: Routing. Online games don't need too much bandwidth but most games benefit from lower pings. Ping is the measure of the time(i.e latency) a packet of data takes to be sent from you to the server & vice versa. The closer you are to a server you are leads to better pings.

Depending on the server load that the ISP has at a present time they might route your packets through various "paths" and depending on that you get higher or lower latencies in your games. Sadly you have no control the way your packets are routed once they leave your PC.