Currently I have 7 (update: 8) gold badges. In Singapore, there's no such thing as easy gold gyms by holding a gym for 20 days. Gold gyms are mostly earned through raids, battling for hours against GRB feeders, and feeding berries.
I'm already considering powering up a Lugia, just for the purpose of sweeping through gyms for gym badge points with potion efficiency. If I run into a Tyranitar or Aggron, I'll just switch to Machamp.
I have broken down those gyms into groups.
Group 1: 5 gyms, 4 gold. The last gym used to be completely "locked out" for instinct. It’s possible now, but I’m focusing on completing Group 3 for now.
Group 2: 3 gyms, 2 gold. The 3rd gym is rather out of the way and somewhat locked out for instinct, so I'm skipping it.
Group 3: 7 gyms, 1 gold. My main gyming and raiding area right now.
Group 4: 7 gyms (1 EX eligible), 0 gold. I don't usually gym here, mostly raiding T5s here because of gym control.
Group 5: 5 gyms (1 EX eligible), 0 gold.
Group 6*: 4 gyms, 0 gold. These 4 gyms are almost impossible for Instinct to survive in. I don't even bother raiding T5s there anymore, because even raid lobbies are Mystic-heavy.
In the old gym system, there were 3 gyms in this area. The gyms are very close together, so it was a very popular gyming spot for a high-turnover area. I used to gym here too.
Most of those gyms (besides group 1) can't actually be seen from my house, but they aren't that far, and that area has strong presence of my team (instinct/yellow, see comment below).