My son reckons 40 MB download speed is ample - the faster, the better though, but the main concern is if your ISP provider is perhaps the only one by all your houses just how fast is it at peak times?
When you purchase your package, they advertise the fastest speed ....not necessary when It's overloaded at peak times..... thats the time to carry out a speed check ...... plus always be aware if BT Outreach are working on a box near you, they can sometime inadvertently reduce your speed by accident fixing a problem for another customer.....