ref ian72's point that I might not actually need anything higher than 17 mbps on my laptop...
That's true, but I went for a higher broadband speed because I believe our increased use of TV streaming in the short-term future would warrant a higher rate.
Of course, the TV signal is wifi dependent because an ethernet connection isn't really feasible. Many of you probably know how to analyse the wifi function on a smart TV but I'm afraid that's a technical bridge too far for me.
Well your TV might support better WiFi than your by your own admission old laptop. So you might get more in total. On the other hand the screen itself often acts as a shield that attenuates the WiFi signal.
That said the basic rule of thumb is to reserve your WiFi bandwidth for devices that are actually mobile or don't have an ethernet port, and wire anything that is in a fixed position and has an ethernet port up. The result is a thousand times more reliable.
At the end of the day no ISP can guarantee any speed with WiFi because there are too many variables, with things like the size of your property, the materials your property is made from, the presence of competing WiFi signals from your neighbours, and other devices like baby monitors in the 2.4GHz band effecting what can be achieved. It's why the basic rule of thumb is to use ethernet if you possibly can.