STOP TYPING IN ALL CAPS! NOBODY IS GOING TO HELP YOU!
Yes, you can mix and match memory brands. It's not the best thing to do, since some IC's dont work well when used together, but unless your getting a bunch of errors or something of the like it's fine.
I suggest you run memtest for a couple hours before anything else, it'll make sure the ram is ok.
The only way to speed up ram is by oc'ing it, but unless you have an AMD cpu and really slow ram, or are oc'ing your cpu it isnt nessary.