I have Optimum Online Boost and have my cable modem connected directly to the back of my desktop computer.
To get the best possible Internet speeds with Optimum Online Boost, do I need a Cat5, Cat5e or Cat6 cable? Which ethernet cable is required? Would a Cat5 cable perform just as good as a Cat6 cable?
Cat 5 is just fine for that application.. You'll see no difference between a 5, 5e, or 6e for what you are using it for. The one that comes with the modem is fine - save your money.
You have a masserati (ethernet) driving on a dirt road (boost). You are limited by the dirt road, not the car. -- NOTHING justifies terrorism. We don't negotiate with terrorists. Those that support terrorists are terrorists.
As others have said, you are already way faster than Boost+ can handle even at 50Mbps. Cat5 cables are 100Mbps while 5E is rated at 1Gbps so either one is already more than enough. CAT6 is not necessary so just save your money.