Yeah thats the standard. I mean there is DDR3 but its too highly priced now.
The tutorial in the hardware tutorial says that you should up by only 5 just in case when overclocking. Do the core clock and the memory clock seperately. Make sure to test it before setting it to "apply when starting windows". I think if you want to be safe start with like a 5% overclock. Its not a lot at all but make sure it works with something like CS:S and then if it works perfectly fine without a lot of heat work up slowly from there.
It can be dangerous if you are reckless to overclock but its perfectly safe so long as you're slow and careful about it. There are usually warning signs before it completely overheats though. You'll see dots appear randomly on the screen.
Like I said I don't know if you'll see any real improvement but if you just need more frames that might just do the trick. Now if you want to increase that detail setting from medium to high then it won't help much.
Thanks.