Surely 80mm is the standard but if it's not that much different isn't it better go with a smaller scope? I'm just thinking how much am I missing by losing 10mm, or is it worth the weight tradeoff.
It really depends precisely why you care about portability. Everyone here will agree that any adult of normal strength can carry all but the heaviest of 80-mm refractors, complete with all but the heaviest mounts, in one hand. If all you care about is taking the telescope outside to your backyard, packing it in a car, or carrying it 100 yards from a car to an observing site, then there's no point in getting anything more portable.
If you plan to travel by public transportation (most definitely including airplanes!), or for significant distances by foot or bicycle, then yes there likely is a reason to think carefully about ultra-portability.
For the record, the rig that I plan to take to South America to observe the forthcoming total eclipse, and to make a full survey of the far-southern sky, weighs 13.5 pounds, or 6 kilos. That includes a camera and binoculars. Strip out the camera, binoculars, and solar filters, and use a smaller tripod, and I could reduce that to 9 pounds, or 4 kg. This rig is based around the optical tube of the 80-mm f/4.4 Orion GoScope TableTop Refractor.
As for aperture, beware of assuming that "almost the same" is transitive! Yes, a 70-mm refractor is almost the same as an 80-mm refractor. Likewise, a 60-mm refractor is almost the same as a 70-mm refractor. But it is absolutely not true that a 60-mm refractor is almost the same as an 80-mm refractor! On the contrary, the views through an 80-mm refractor are much brighter and more detailed than the views through a comparable 60-mm refractor.
The elephant in the room throughout this discussion is what I like to call the "cuteness factor." Some telescopes are just irresistibly cute, regardless of their actual size, weight, and usefulness. My 80-mm GoScope is irresistibly cute. The classic 90-mm Questar is irresistibly cute -- considerably cuter than its knock-off, the ETX-90, though that scope is pretty cute too. The TeleVue TV60 is irresistibly cute. Many spotting scopes are irresistibly cute. Even the 4.5-inch StarBlast is arguably irresistibly cute, although it weighs and bulks more than many telescopes that don't seem awkward and ungainly.
Edited by Tony Flanders, 18 June 2019 - 05:25 AM.