That's not my logic at all. If a train can do 90, 100, 110, 125, 140 but the speed limit is 75, then they can ALL do only 75.
If a train can only reach 75 but in reality at a push can hit 90, and the limit is 100, then is that speeding? You're saying it is, which is fair enough - but I am not ever suggesting that trains that can go faster than the line speed isn't speeding. Not sure how you can take that from what I've written either?!
My point was that the speed limit for a train is the lowest speed allowed by the line, traction, load, isolated safety systems, weather conditions and possibly other factors. Going above the lowest speed out of all that is speeding.
Why would a unit be designated a maximum speed at all if it is ok to ignore it? The fact that 313s mainly work on lines below 75 is coincidence or perhaps more that they were built specifically for those routes so designing them for higher speeds is pointless but they still regularly run (several times daily in fact both empty and in service) on metals up to 125mph. But they are still 75mph units so even when running fast line from Hitchin South to digswell (as some do in the early morning) they can't exceed 75 any more than a 100mph 365 can exceed 100 on that same bit of track.
I'm slightly confused as to why you would think that a trains maximum design speed is optional and ok to be breeched when you don't seem to think it acceptable for a 365 to do 125 on the fast lines?