I have exactly the same problem, too.
Everything works fine as long as the files aren't over 150 MB big in size.
I can't upload them to my ownCloud via browser upload, sync client or WebDAV (using Transmit on my mac).
Transmit only reports: Could not send request body: connection was closed by server
I tried to change all necessary values in the php.ini (like timeout, memory, max input time etc) and even increased my Apache's timeout to 1800.
Nothing helped at all. And yes, I have restarted apache
Any more ideas out there?
(ownCloud 5 Beta 1, Apache/2.2.16 (Debian), PHP 5.3.3, MySQL 5.1.66-0+squeeze1, ownCloud Mac Client 1.2.1)