UPDATE: servers are back online, so zones are going to change now.
All Zones 1000+ confirmed possible. Time to explore new boundaries.
Green Hill Zone 1000+ and 1100+ confirmed possible.
Jungle Zone 1100+, 1200+ and 1300+ confirmed possible!
Mechanical Zone 1000+ and 1100+ confirmed possible.
That's right, we're in quad digit rings now!
Green Hill Zone best: 1190 rings w/Neutral Super Rare Chao (Amy)
Jungle Zone best: 1371 rings w/Neutral Super Rare Chao (Amy)
Blue Sky Zone best: 1038 rings w/Neutral Super Rare Chao (Amy)
Mechanical Zone best: 1100 rings w/Neutral Super Rare chao (Amy)
If you wanted to try this, I'd recommend upgrading your Fever to level 5 & keeping it there, you'll see why if you play the game. Also I recommend using the Neutral Super Rare chao in the series that collects rings. If you really wanna do it right, you need to predetermine ONE character you want to use for RA and upgrade ONLY their stats until you'd go to level 6.
I can supply screenshots of any of these games if needed.
UPDATE: New verdict, any Chao is allowed for RA competition, the only thing not allowed for RA competition is the Ring Streak booster.