by Usman Asar.
Eugene, have you not tried running 64-bit PHP 5.x? Though experimental, but I have ran 64-bit 5.x on IIS absolutely fine.
just for the test, you can install 64-bit side-by-side and try making backup and see if it still limits, if you're unsure of setting up multiple PHP's on IIS, then watch this video, setting up PHP with PHP Manager. http://goo.gl/RKSpQJ