is your issue solved?

You may check in the router's admin page to see whether it have the option for Access control. If it does, then you can try to set it up for your purpose.

All the IPs in the range will share the bandwidth of 200Kbps for the rules you set up. You can get more details about the bandwidth control setup in this link: http://www.tp-link.com/us/faq-557.html

The remote management occupied port 80 by default. You may try to change the port of remote management under Security-->Remote Management to another one, then try to open port.

Is the slow speed with wired connection, or wireless connection? If the slow speed is for wired connection, then normally we can just upgrade firmware and reset. For C3200 2.4G issue, you may check...

May I know which firmware you are trying to upgrade? Since you are from UK, you may go to the UK website to get the corresponding firmware : http://uk.tp-link.com/download/Archer-D2.html#Firmware And...