i thought overclocking the core gave biggest benefits... and memory didnt help very much,
Well I only said this because not only of the articles I read regarding video card overclocking, but also in my personal experience you can usually push the core up much further than the memory and I've always noticed the biggest difference by changing the memory speed.
Of course you'd think the core offered the biggest increase being that it's like overclocking your CPU.....but generally if you overclock your RAM or even put in faster RAM you'll notice a nice system increase in speed whereas you really won't notice THAT much increase in overall system speed simply by overclocking the CPU..
Could depend on the card itself too...architecture of the card, perhaps your system isn't set up the same as joe blow down the street, a variety of things.
It's just simply what I've read and experienced that the memory will offer you the most boost when OC'ing it, but the memory will generally not go as high as the core since the core atleast has a heatsink on it whereas the memory (except of course for the 6800's and whatnot) don't have any cooling on them.