Generally speaking, it’s best to enable both IPv4 and IPv6. This allows your computer a greater range of connection options, and your computer has the capacity to choose the best option for any situation. As for an onboard NIC, you should usually enable that so that you can use an Ethernet cable if you want.
If you turn off SpeedStep, the processor will run faster at the cost of consuming more energy and creating more heat. If you want a faster computer and are ok with these trade-offs, it might make sense to turn it off. If you value power efficiency or want to extend the lifespan of your CPU, it’s best to leave it on.