I think 300 as a climbing speed might be a little high :o
I am not sure what the scale is but the climb speed is determined by a sliding scale that is relevant to current altitude.
300 as a climb speed might keep your passangers to the seats like astronauts going to heaven...
Actually, what would keep anyone glued to their seat like an astronaut would be acceleration, not velocity. That is not to say that velocity isn't important, just not the effect that causes you to experience increases or decreases in G-force. For example, if you are traveling at 1,000,000 MPS but only accelerating at .01MPS
2, you would probably be unable to sense the acceleration at all; the perceived G-force would be very close to 1. However, if you accelerate from 0 MPS to 100 MPS in 1 second (an acceleration of 100MPS
2, you would feel and incredible about of G-force (roughly 10 G!!!).
Now, aircraft are subject to other stresses besides just G-force (acceleration) that are related to their velocity. Lift, friction, turbulence, and air pressure all act on the structure of the aircraft and can be affected greatly by velocity. So, while your passengers may not be able to feel excessive velocity if there is little or no acceleration (they aren't glued to their seats), the aircraft itself may suffer considerable structural damage over time and eventually fail.
One final note, if a vehicle goes ballistic (that is, accelerates directly against the pull of gravity), there would be a definite increase G-force as any ballistic acceleration will be 1 (gravity) + the G-force of the acceleration. Again, velocity is not the issue here, so much as is the vector, or direction, of travel. The steeper your pitch, the more the Earth's gravity will add to perceived G-force increases from acceleration.