It's called 'new learning'. Welcome to the world of a beginning Moodle server administrator! Congrats! You've gained on it but you've learned some things that apply to InMotion hosting VPS boxen - different world on RackSpace dedicated machines. It's a journey with no end. ;)
There's one thing you've not tried for uploading 450MB files ... the 'backdoor' to the Moodle file system ... File System Repository.
http://docs.moodle.org/26/en/File_system_repository
In moodledata create a folder called 'repository' and set ownership/permissions like those of other folders/directories at that level (ie, in moodledata). Inside 'repository' create another directory called 'largebackups'. Set ownership/permissions just like the repository folder.
Using your newly discovered FTP tool, upload your 450MB backup file into the repository/largebackups/ directory.
In the Moodle, create a category called 'Course Restores' and inside that category a course called the same thing. Nothing fancy in that course cept setting up the file system repo pointed to 'largebackups' in that course so you can see those large files without having to upload via Moodle UI.
Start a restore process in that course. Select the File System Repo resource ... the 'largebackups'. You should be able to see your large backups and restore to a new course - do NOT restore to existing course as you want to keep the 'course restores' course for future restores. It's the only one that needs the File System Repo set to 'largebackups'.
'spirit of sharing', Ken