IB is a crapshoot really. I've installed maybe two dozen 3570k and 3770k chips now for various builds, and some happily hit the 4.7-4.8Ghz range (rare), some won't push past 4.2-4.3 without more volts than I like (also somewhat rare, but more common), most seem to float in the 4.3-4.5 range with good push/pull air cooling, 4.4 seems a sweet spot without volts too high. I'm pretty conservative with overclocking though. I had one 3770k that was unstable at stock (!!).
I wouldn't worry about changing ram settings, that just introduces more headaches for not much gain on your config. With Llano/Trinity you get huge gains from ram OC, for SB/IB the gains are minor in comparison.
Normally I tell people that overclocking much on IB isn't worth it, but with SLI 670s, you probably will see solid gains all the way up to 4.4 on very demanding titles such as Guild Wars and *cough* Civ5. So if you play any CPU-bottlenecked titles that are bottlenecking below 60fps (or 120fps if you run a 120hz LCD), then go for it!
I will still say that whatever wall you hit, back it off at least 100Mhz for safety, and in my book, near-stock volts is the way to go. 1.3v is my absolute ceiling on IB, but I'd rather see 1.26-1.28 as max. IB is still too young to know if we're going to see a rash of dead ones from overvolting maniacs.
Going back to the first point, it's really a true crap-shoot compared to SB, which was much more predictable overall.