Ah, I see. Well I got 1.2v on my stock BIOS that came with the card, then since I couldn't back mine up when I was flashing it to the modded BIOS, because of an error, someone uploaded their stock BIOS for me. On both my BIOS, and the other guy's stock BIOS, I got 1.2v. So maybe it's the card itself that won't let you hit 1.2v, because I got it on 2 different stock BIOSs. I'm not on the computer I have to the BIOS saved to, so I can upload it in a little bit if you'd like to try though.
The core Boosts to a different value on each card, so your +100mhz offset will give a different core clock than others. That's why we usually talk about overclocks with the final clock and not the offset, because a particular offset gives each card a different clock.
Precision displays the memory at the DDR3 speed I believe. So you have to multiple it by 2 to get the effective speed, which at stock is 6000mhz (or 3000 x 2). When you put +100mhz on the memory, it's actually +100mhz on the 3000mhz that Precision is showing, so the effective, final value will be 6200mhz. So basically, when working with the memory, multiple each value by 2 to get the effective speed.