Aperture is not the only decision
Larger aperture collects more light, but astrophotography also depends on focal length, camera sensor size, mount performance, and guiding tolerance.
Wide targets favor shorter focal length
Large targets such as the North America Nebula or Andromeda Galaxy are easier to frame with shorter focal lengths. This also lowers the difficulty of tracking and guiding for a first setup.
Small galaxies require more reach
Small galaxies and planetary nebulae need longer focal length if you want scale. That choice also increases sensitivity to focus, tracking error, and wind.
A practical buying rule
Choose five targets you actually want to image, then check their field of view with your camera sensor. That workflow narrows telescope options faster than comparing specifications in isolation.