I think at this point the OP would have taken the security over the extra speed! However, UPS and FedEx are reliable - many embassies use both services to ship out Visa'd passports when working with them. That being said, in a previous life, we always shipped out important legal documents on UPU Registered Mail since we'd have a receipt of delivery. In the hundreds of packets I shipped out using Registered Mail, none of them were lost and twice we received them returned (wrong address in South Korea). One thing to keep in mind is Registered Mail works even for international mail. There were numerous legal documents I had shipped to the US, Asia and Europe and had 100% tracking from end to end (including when a document was delivered to a remote city in Deutscheland).

Safe Travels,

James