You have a perfectly good connection speed now for your exchange. Before you go to the upheaval & expanse of changing ISPs and/or switching to Fibre get yourself an Ethernet cable to connect your Mac to the router, if at all feasible, and see the difference. I think you will be surprised

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1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 20 Meg WBC