Ok, first thing is I'm not quite an expert, but I have read tutorials and such on this. As they always say, nobody can tell you exactly how much to OC, but I think I can give you some suggestions.
A general idea is that you shouldn't go above 33% of your core clock.
The RAMDAC is simply your video card's ram which is built into the card, thats the 128mb it says in the title. This can usually be increased more than the clock and it is very effective in speeding things up.
Now, seeing that you have an Nvidia card, I suggest you get something called Coolbits (if you don't already have it or something else). This is a modification to the Nvidia control panel which adds a setting for GPU clock and memory speeds. Once it is loaded, you will have a very simple interface for OC'ing which consists of two bars.
The process of overclocking is a series of increases and tests. You move the bars up and test your results. Generally, after you have your card set to a speed you like, run a graphically intense game for about 5 minutes and check for performance and any errors in the picture (artifacts or such). Try to raise the bars in about 10mhz increments for every test. Once you have problems, lower the bars about 10-15mhz and you should have established your best safe overclock speed

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I'll give you my best numbers a little later.