just stick with what coolbits overclocks your card as, dont increase it, make sure your fan is always running, if you get into a game and see artifacts like squares or the screen looks weird shut down immediately, thats about it, just keep that card cool and stick with the overclocking defaults that it gives you and you should be fine!
just cause he has a lot of ram doesnt mean its fast, you could have 1gb of 800mhz ram and thats better than a ton of slow ram, as far as oc'ing your 5200 i have one, doesnt work... at all, but give it a try, using coolbits