Hi, just thought I'd share my experience with my internet upgrade from 300 to 600. 

My internet 300 had been rock solid- always testing above 300. Never had any issues with it. When I upgraded to 600, I got the new gateway wifi modem, which I liked a lot because it covers my entire house with 5GHz, whereas before I needed a second router to cover the entire house.

However, my hardwired PC speed actually dropped. It was around 300 on the first day, 600 on the second day, but starting from the 3rd day on was 150-250Mbps. 

Tried technical support online and by phone, and they eventually sent in a tech. The tech determined that the installer had not put a "MOCA" filter on my line, and also the top high frequency bands from the curb were not strong enough. He put the filter in and put in a call for the bands.

He then factory reset my modem because it was not giving him more than 300Mbps on his equipment. After the reset, the wifi speed was around 500Mbps, but my hardwired connection still 200. He said it's something with my PC  - not Shaw's issue, which I agreed with.

The next day the shaw guys were outside on the poles, I assume fixing the levels, but I have no way of checking that.

My 5GHz wifi connection was fine around 500Mbps to laptop, but PC still bad.

Today, I downloaded and ran "TCPOptimizer" from speedguide dot net, and rebooted my pc, and it's now running 400-600Mbps consistently. 

So, in the end a combination of issues but I am finally up and running.