I spent many hours looking for 60x10 and 40x10 fans for use in a SFF PC I have. See my earlier post
for my experiences. As I'm located in the US, I wasn't able to get any Papst models.
I've also found that the noise level made by small fans is drastically different in free air vs. mounted, especially with 40mm fans. This seems to be related to the size of the exhaust opening for the fan and not the rigidness of the mounting or anything like that.
I think your best bet is just to undervolt the fan you have. Just make sure it starts reliably at whatever voltage you choose to run it at.