It appears several people here have been having problems with downloads not fully downloading (download finishes early, usually at a similar filesize).
In my case this seems to be related to the speed at which the download happens (and thus overall length of time taken to download).
Works fine over my 15megabit connection but not if i limit my download speed to say 500kB/s.
I have tried increasing both the max_execution_time (now set as 1800 seconds) and the memory_limit (set to 512MB - downloads are ~300MB) however this has not imporved the situation.
I noticed that the Download & Donate plugin features support for mod_xsendfile:
Would you perhaps consider adding support for this?