No problem, just wondering. Its odd that you end up with 500 Mb/s via wifi and only 250 Mb/s via ethernet. The MacBook Pro has thee wifi antenna, so the wifi data rates with the MacBook Pro should be better than the typical laptop. I don't understand the lower ethernet rates, unless there's a problem with the ethernet cable or port connections. Very strange indeed. The wired rates out of the modem or thru the follow on router should be the same.
Ok, just out of curiosity, is the XB6 modem running in Gateway mode or Bridge mode, and is the Google router running in full router mode or Access point mode?
What they should be configured as is as follows:
1. XB6 in Gateway mode ---> google router in Access Point mode
2. XB6 in Bridge mode ---> google router in full router mode.
Now, if you happen have:
XB6 in Gateway mode ---> google router in full router mode
what you have is a protected zone within a protected zone, and you have a double Network Address Translation (double NAT) situation running, where the XB6 runs the translation from external to internal address, and the google router does the same. If you're not doing anything that needs port forwarding or high speeds, like gaming, then you can live with that configuration. Its not ideal, but you can run your network and possibly not see any problems.
There is always the possibility of some issue with the google router which might boil down to some setting that results in slower ethernet performance. That would be a little strange, but, one has to keep an open mind when it comes to network issues.
If you run a wired test thru the modem and ended up with 500 Mb/s, that would point the finger at a google router setting or port problem, which could be a WAN port or LAN port problem.
Just for test purposes I'd kick the modem into Gateway mode, then connect directly to it and run a speedtest in that configuration. You should be able to see 500+ Mb/s thru the modem. If so, then the question is, whats the issue with the Google router. Don't know what you're using for a speedtest site, I recommend the www.speedtest.net Toronto Vmedia server these days.
When thats complete, kick the modem back into Bridge mode and reconnect the google router.
Ok, but, you're seeing 500 Mb/s thru wifi thru the google router, but only 250 Mb/s via ethernet thru the google router, correct? If my interpretation is correct that indicates that the modem is connecting to the google router correctly, otherwise you wouldn't see 500 Mb/s via wifi thru the google router.
Assuming that you see 500 Mb/s thru the modem, with an ethernet connection to the modem, that takes the modem and MacBook Pro out of the picture. The question at that point is, whats the issue with the google router?
Has there been a recent update to the google router or the MacBook Pro?