I suspect the above poster suffers from what is called "Aperture Fever". It is probably important to point out the original poster that these two scopes have very different focal lengths will be suitable for very different targets. This is a product of their vastly different fields of view. I suggest plugging both into a simulator and framing various targets they may be interested in imagining. Astronomy.tools has this ability and is online for you to plug in equipment to use. I also like and somewhat prefer telescopius.com.
Field of view is a product of focal length and sensor size. Using an APS sized sensor on a 800mm scope and targets like the North American Nebula or Andromeda are simply too large to fit. With the 400mm Esprit they are perfectly framed. Upgrade from the DSLR to an 4/3" or 1" astro sensor and the problem worsens. This means the larger aperture will need multi panel mosaics on these popular targets. Something most beginners do not need to deal with on year one of this hobby.
How fast the light is collected is not directly tied to aperture. It is more directly tied to the focal ratio. The f/4 Newt will collect light at a faster rate than the f/5 refractor, but not because of the 8" aperture. It is because of the focal ratio. My 12" SCT at f/7 has a lot more aperture than either scope but will collect light slower and will need longer exposures. If my 12" SCT needs a 120 second exposure, the refractor will drop that to about 60 seconds. If you refer to a f stop scale it is one full f-stop between f/7 and f/5. Each stop doubles or halves the amount of light per pixel. Using the same charts it is 2/3 of a stop down to f/4. So your exposure will drop again but not quite in half...math is 40 seconds.
As I stated earlier in this thread the Newt with its larger size will demand a lot more from the mount than the refractor. It is certainly possible that the EQ6 mount that you receive will be above average and provide tracking sufficient to image well with it. It is also possible it won't and that you will struggle and get frustrated and either give this venture up or be faced with replacing it with a more expensive mount. Now I will fully admit that I have no first hand experience with this combination, as most here don't.
I fully admit to being afflicted with the aperture fever when starting imaging. In hindsight I will tell you this, the large apertures will cost more money and not in a linear way but much more logarithmic. The increase in image quality will be marginal if at all and lastly you will learn faster and spend more time imaging with the Esprit if you somehow won the lottery and had both scopes at your disposal. I myself send much more time imaging with my 4" refractor.
Edited by idclimber, 11 June 2021 - 11:59 AM.