People assume that a blazing fast 340 Mbit/second cable modem will give them better performance than an 80 Mbit/second modem. "4 times faster! 8 times faster!"
All of that talk is simple marketing garbage, a hold-over sales pitch from the days of dialup modems.
The fact is that the Internet doesn't work like that. You will likely get the same exact performance with a low-cost standard cable modem versus an expensive fast modem.
The reason? Internet bottlenecks. The Internet is a vast, shared network, and there are plenty of bottlenecks on every network path. With your 340 Mbit/second modem, you'll know that your modem is no longer a bottleneck. But there are more than a dozen network devices between your computer and Google and so your cable modem is likely never the slowest device on the network.
What other devices are slowing things down? First, there is your home WIFI. Then there is bandwidth that your ISP provides to you. Then there is the network equipment at your ISP, which is shared among perhaps hundreds of thousands of users. Then there is all of the shared networking equipment between your ISP and Google's ISP, which is used by millions of users. And then there are all of the network devices at Google - which is used by hundreds of millions of users.
Save your money. Get a normal, reasonably priced modem, like this TP-Link DOCSIS-3 Modem, or this Netgear DOCSIS-3 Modem. Your performance experience will likely be identical to a "blazing fast high performance" modem, and you'll save a ton of money.