Increasing the PCIe freq. is hit or miss I guess; I saw no differences when I did it (tested several intervals between 106-120). Some have reported success with it, though.
The sweet spot you will want to reach on the core is 700MHz, since around that frequency is when the most performance increase is achieved. After the 700MHz mark you may start getting diminished returns, as smaller and smaller MHz increase require more and more volts. It will depend on your core, of course. For example, say you can do 705MHz @1.475V but it takes 1.550V to go to 715MHz; not worth it since the only thing that will increase will be temperatures.
Memory is a bit trickier to OC. I found out (thanks to the guide I posted earlier) that VDDCI is the one that allows you the most increases in memory frequency. What's even better, is that VDDCI doesn't seem to add much heat to the regulators and the card in general, as opposed to MVDDC and MVDDQ. At 1.580V I'm able to take my memory to 1035, while keeping the other two at modest levels (2.113V); contrarily, if I keep VDDCI at stock I need about 2.236 on the MVs to achieve the same speeds. The trick is finding the combination that allows you the highest OC at the lowest temperature.
Also, keep in mind that increasing these voltages will increase the overall power draw of your card. At stock my card draws about 27-29A, and now that I have increased the voltages it draws around 32-33A; it also "eats" through 0.2V of my 12V rail
. A power hungry beast, but I love it