the bigger the tv you buy the more issues they normally have (LCD's).
e.g. the 50 inch could be perfect but the 65 inch of the same tv could have horrible banding, etc.
a mate at work dropped £3.5K on a tv iirc and he had it swapped out several times before getting a refund and opting for a smaller and much cheaper model.
ideally you would be best keeping your ST50 and buy a projector, spend the majority of the cash on the projector as you can upgrade the screen easily at a later date.
then when your st50 is on it's last legs (4-7 years time) will be the time to buy OLED once most of the niggles have been ironed out.
also that cnet article is hardly gospel in fact it sounds ridiculous.
i'm 8-9 feet away from my 50" and there is no way i would want anything bigger at that distance, my friend has a 60" at a similar distance but it's far too close IMO.
https://www.avforums.com/styles/avf/editorial/products/38c56aa3af5093a6cc7282bb9bf5eee8_0.jpg
use that as a reference it's pretty clear
https://static.avforums.com/styles/avf/editorial/block/0321276f9acebf132084b7608928bb54_3x3.jpg
that also but tbh forget the degrees and use the top one
65" the closest it should be is 2.5m, you can have it closer but your not getting any more benefit that at that distance
75" and the closest it should be is 3m, you can have it closer but you won't be seeing any more details
the opposite is also true the biggest distance away on a 65" should be 3.8m after that you will lose some details nothing major but some people may notice more detail at say 3.8m than at say 5m
so their are optimum distances to have your tv but it also depends on your eyesight and good your vision is. you could put a 200" in front of a blind man and it won't make any difference compared to a 5" screen for instance.
so the best question you could answer is how far away is your couch from your tv stand? has to be roughly accurate don't guess if your not sure. i know my distance because i have a double bed (roughly 6 foot long) plus a 2-3 foot gap to the tv (bedroom setup).
so my 50" is 8-9 feet away and the optimum distance is anywhere between 6-10 feet on that chart for a 50" so i know i'm not missing out on anything and i know it's not too close.
personally though at this distance i don't think a bigger tv would really suit