I just filled up my car (M54) engine with RON95 as per the manual (Research Method fuel apart from RON 98). Since my M54 engine has a knock control function, it can run on different grades of fuel. With regard to RON 91, my manual recommends me to use it only in exceptional circumstances.
I have a very good first impression on RON 95. The engine immediately feels quieter. This is very evident. Performance wise, on the highway I can't tell the difference from RON 97. After all, all the performance and fuel consumption figures are based on RON 98. Based on my manual, RON 97 is like neither here, nor there. At least RON 95 is Research Method fuel. Probably, this is the reason why the engine is quieter. Apart from this, I feel my consumption feels better with RON 95 compared to RON 97. This is just my initial observation. To be confirmed later.
I heard in Thailand, there's no RON 97. Only RON 95. So, I guess it's OK to fill your car with RON 95.