Not getting the advertised speed of 600 Mbps. Is this right ?

I upgraded to supposed get "up to 600 mbps".  I get spurts of 420, with the final results in the 350s.

Is this normal ?  Shouldn't we get what WAS ADVERTISED ?

I've been to get support - and the automated options keep resetting my modelm and gateway.  And then it drops you - whether using chat or phone call.

BTW, I'm using NETGEAR CM500V Cable Modem and was speedtesting with WIRED to it !  The product supposedlly can do up to 680 Mbps.