Agree with that, and that's why I think 57-58K would be a good starting point. It would put us in the same bracket as Spurs, Arsenal, West Ham, and notably above Man City and Liverpool. The Geordies would be long forgotten about how great their fans are as they fall down to about 9th biggest Stadium in the country. We have to be aiming to be joining the Arsenal's and Spurs' of the league and not just marginally going ahead of unsuccessful yo-yo clubs like Newcastle (talking last 80 years, as I am well aware historically they enjoyed some success in the early years).
After seeing the trend of other clubs moving to new grounds and the significant rise in crowds, our impressive historic attendances, and the sell outs we've been getting in the past couple of years, I think averaging 55K would be quite comfortable so even if there were a couple of thousand empty seats it wouldn't be too noticeable in a 57-58K stadium. If it was 60-61K, it wouldn't look great and the atmosphere could suffer.