The trajectory calculations take the stated acceleration value into account. The only virtue in telling Mach3 about a high acceleration value is to get faster movement.
That depends.
In CV mode, Mach3 tries to maintain a constant velocity. Physics dictates that you can't turn around a corner without decelerating, and then accelerating back up to speed. In CV mode, you are telling Mach3 not to slow down. So when Mach3 gets to a corner, in order to maintain that velocity, it starts making the turn before it gets to the corner, rounding the corner off. Acceleration dictates when Mach3 starts to make the turn. The faster the acceleration, the further into the corner it can go before it turns, resulting in less rounding.
Try setting stop CV to a lower angle.
I already resolved this issue at CNC Zone a few days back.
Stop CV on angles only works when you have two moves at an angle, say a square with 4 linear moves.
Most CAM programs will create toolpaths that roll around the corner, so they have 4 linear moves with 4 arcs at the corner.
So your toolpaths are straight segments with tangent arcs at the corners, so there are no toolpaths at angles to each other.
Thus, Stop CV on angles will have no effect. If the accelertion is so low that Mach3 can't follow those tangent arcs at the corners, it will start turning the corner earlier, rounding it off. This is the issue that the OP had.