An exception is thrown when trying to receive a file of 17MB, other smaller files are ok. I expect to be able to retrieve a file of this size, because Salesforce support upto 25MB and the REST api supports the same.

When using the camel endpoint "salesforce\:getBlobField", to retrieve a file of 17MB. We are running in Openshift, but I can recreate this problem outside the OS environment from within a JUnit Test running the route, within Eclipse on my Machine. The same test passes when I change the AttachmentId to that of a smaller file in Salesforce.
I can successfully, within a JUnit Test, use the salesforce REST api (omitting Camel) to download the same file