I'm working on a 11 minute video using both Sony E3 HD 30 fps footage and Canon 5d footage in 30 as well. When rendering I get the "out of memory" message all the time. I shut down the program and restart and everything works fine for a while and then the same.
I have a 2 x 2.93 Quad-Core Intel Xeon with 28 GB ram. The footage is on a external SATA connected drive
Convert all your footage still in the H.264 codec or whatever into ProRes 422.
Footage straight out of a DSLR is in no way, shape or form in an acceptable editing codec for FCP. The reason: such footage is far to processor-intensive, something that a formidable amount of RAM can't help, and in sufficient amounts, it will bring FCP to its knees. FCP remains a 32-bit application, and can access just so much memory.