Vacillating Speed Tests.

I have windows 20H2 64 bit and run a speed test now and then. It is 40 Mbps at times then 450 Mbps and does this ail the time. I use Ethernet. Comcast rewired this building of 800 residents last winter till the virus hit.
Comcast and I have troubleshot this to death. I have plugged my new modem(theirs) into the wall. My current setup is a surge suppressor with 8 devices in it on a 15 amp circuit. I have the pc. speakers, monitor, phone, printer, small lamp on the strip. The strip is old and I don't expect protection just a means of plugin devices in as I only have one box with two receptacles. I used another adjacent box for a lamp but it is likely on the same circuit. Comcast says it has issues then says it is ok.

Question, why does speed test vacillate between my contracted 600 Mbps and 40 Mbps?
I replaced the cable to cat 6a. Would a surge suppressor make a stabilizing difference.

 

So which speed are you measuring, the speed available to your router or the speed being reported by an online speed test? The contracted speed of 600Mbps is entirely Comcast's responsibility but the speed you see when using an online speed test is your responsibility unless your Comcast supplied router is faulty.

 

@Earthling - I was running various speed tests other than Comcast's thinking C-cast would enhance their speed on their end.

@TimW - I began to use the speed test within Comcast that you show in the link you provided.

@Both - had I come back to see your pasts I could have saved myself some time. I have used the speed test TimW has referred me to and it consistently shows speeds of over 600 Mbps which is my contracted level. Either they are embellishing their speeds or their tester is accurate and giving me great results. I guess you have to trust someone!

Btw, I get no notification that someone has posted here when I ask a question. Is that normal or did I miss a setting?

 

Check your settings.

 

Thanks Eldon. All of MG's was going to my Gmail spam folder. I just corrected it and it's the reason I am here now.