Having looked through 10"ers and 12"ers many times, I'd say the difference is not worth the extra money and bulk (you do mention portability) based on the visual improvement. I've owned the 10" and 8" versions of these GSO dobs (still have the 8") and noted that the 10", while an excellent general purpose visual instrument, was quite a bit bulkier than it needed to be. Granted, it wasn't much of a problem at the time because I didn't have to travel with it. Also, I was still able to lift and carry the whole thing by myself (just). For some reason the gap between the mirror edge and the inside of the OTA was much wider than in the 8". The OTA was almost 12" outer diameter if I remember correctly. Mount sized accordingly. The 8" is much more portable than the 2" difference would suggest. And these were two scopes of similar focal length. Now, with the 12" vs. 10", you are adding 250mm of focal length on top of the extra diameter and 10kg of weight (30kg vs 40kg total weight). This is a considerable step towards a sore back and away from frequent happy use if you need to take it anywhere but your own backyard. YMMV of course, but will be less with the 12" if you count actual scope carried miles
