Hi Simmo,
If this is for visual, then I would suggest binos first. Keeping in mind that when we use both eyes to observe at night, by the way our brain works the resulting image is brighter than when viewing with one eye only.
The best example I can give is my own experience. I have an 11X70 pair of binos. The closest single aperture I've been able to give me as close an image as these binos is 100mm. 80mm is to small - tried that first and then went up to 100mm.
I had a 10X50 pair first, until they were damaged. In looking for a new set, I did contemplate 25X80 binos. Several factors led me to drop these for the smaller 11X70:
* 25X80 are big. Too big to hold for too long in your hands, and too much magnification to be stable in your hands.
* The true field of view in 25X80 is small. The wider field of the 11X70 makes them more versatile for both astro and terrestrial. Coupled with the lower magnification, makes for stable hand held viewing.
* The net aperture gain is not significant enough to overcome the smaller exit pupil of the 25X80. 11X70 won there again.
* The size and bulk of 25X80 makes finding a suitable mount for difficult. The 11X70 being smaller & lighter, and the lower magnification allowed me to use what I already had to make a very suitable tripod mount for it. The photo tripod I have would not have been suitable for the 25X80, meaning even more expense, and a bigger and heavier tripod/mount again. Not great if you are travelling and space and weight are at a premium.
Yes I do have a 100mm f/5 refractor, and I do use it more frequently than the binos. But, they are different creatures for different purposes. The refractor is bigger and heavier and less versatile than the binos for travelling. On the occasions I go bush with the family, the binos are all I take and I'm as happy as a pig in mud,
I certainly do not feel these 11X70 binos are inadequate aperture wise either. I've managed to resolve Omega Centauri with them, and it is extraordinary how many galaxies you can see with them. As far as rich field scopes go, I wouldn't trade them for 15X70 or 25X80. What this set gives me far out strips anything the other binos can offer.
Just be careful where you buy your binos from. A mate of mine got his 11X70's cheap from ebay - flaming disaster they are. Field of view is narrower, and the distortion of the image starting from 60% out from the centre is appalling. Mine were not overly expensive either, house branded from Andrews Communications. But they perform very, very well, sharp across the whole field of view, and generous AFOV and eye relief.
I also made a very simple mounting block for it to couple it to my existing photo tripod. That miserable 'stalk' mounting block is more of a hazard than a help. That stalk leaves the binos way too high above the altitude pivot point of the tripod head, making it not only unstable, but you need to overtighten the tripod clamp to get the thing to hold. The block I made uses this same stalk, but attached in a different way. It is nothing more than a plywood off-cut that holds the binos in line with the pivot point of the tripod head. I've attached the mounting block of the photo tripod to one end of the plywood and the bino stalk to the other. The tripod mounting block is easily removable so I can use it with a camera. I've worked out the centre of gravity of the binos well enough and positioned it on the block so that I can now leave the clamp totally loose and point the binos to any angle in altitude, including directly vertical, and the binos don't move - totally impractical in this situation, the vertical, but it shows what a little bit of thinking and tinkering can do. The photos below shows the binos rig I use. Best of all, it cost me nothing to make,
weighs next to nothing, and makes use of what I already have.
Some food for thought.
Mental.
PS: My post while a suggestion, I hope it will cause you to think about what you want out of the gear, and some of the pros and cons. A scope could be just fine, but there are trade-offs with any piece of kit - eyepieces, finders, mounts, cables and power (if an eq mount), portability (stowage, weight, complexity of set up and take down, even robustness), visual capabilities (aperture, focal ratio so magnification and FOV particulars), versatility (terrestrial & astro). All this for both binos AND scopes. I'm also working on a 114mm f/4.4 travel scope. Very different beastie to the 11X70 binos, and will be more complex to set up, but offers different things too. No one single correct decision.