They may well be right, I've not been on one yet, they only ran the first unit up just before Christmas. It would make sense if they were only 75mph capable as the Goblin has a low line speed. Think it's around 45-50 but don't quote me on that.
Whether they are is one question, and if they are, whether WMT/Angel do try and change it is another. That may explain why one unit sat at Ilford for 6 months.
75mph would be okay for the Leamington & Nuneaton branches as things stand, but I'm not sure about the snow hill lines or which other lines the other units will end up on. It'd make sense if they were 100mph so they could work with the existing fleet up here
It does say on Angel's website that the /0's have a top speed of 75mph. They own them so I'd say that's pretty reliable