Velocity is imperceptible, since it depends on a frame of reference. For example, I'm traveling at about 700mph around the center of the Earth because of the Earth's rotation.

Acceleration is perceptible, because it is felt as a force. So it really depends on how quickly people are accelerated to 2500mph. If you accelerate at 22mph per second, this is equivalent to 1G, which could be relatively comfortable. It would take 2 minutes to reach 2500mph.

I imagine you accelerate evenly for the first half, turn the chairs around and decelerate evenly for the second half.