I would stick with 28cm - 33cm is a bit overkill in my opinion. It's 13" diameter! There are very few syrians who need anything bigger than a 28cm diameter wheel. I only had the 12" silent runner because it attached to the bars
Our last Syrian was huge - really big - 225g and very big all over. The 27cm wodent wheel wasn't quite big enough for him but the 28cm wood wheel was just right.