That's definitely not fast enough.
That's why, when we talk about HFR in a business context, I say that's not what would lead people to switch to a train rather than driving or flying between Montreal and Quebec City, as you suggested. Speed is the key factor, and I would add that the emphasis should be on travel from downtown to downtown.
For Montreal and the other cities, downtown to downtown high-frequency, and particularly high-speed rail might well lead to expropriations, which would require a lot of work.
If there is to be a modal transfer, I would suggest factoring in downtown to downtown travel time.