Ermm, yes you can Mix. You mentioned PAE yourself & I've used it with Linux - 8GB RAM on 32-bit. For many distros if you have the RAM and choose 32-bit a PAE enabled kernel is automatically used.
PAE = 36-bit..... and its not some secret switch, its something that's very much not to be used unless you know what you're doing !
You won't get more than 4GB per process on 32-bit no matter the operating system.