I was able to get it to 1866mhz with:
CL: 10
tRC : 10
tRP: 10
tRAS: 30
I'm not exactly sure on how to set the timings. Do you edit each one to see how low it will go starting with CL? I couldn't get my clock speed any higher, so 1866mhz was my fastest. I found the max clock speed by setting the timings to 10-10-10-30, not sure if I did this correctly. I heard you are supposed to find that max first then move on to timings.
I have the same 8GBRL kits. I bought a second one after finding out late last year from one of our forum colleagues that you could run them at 1866/10-10-10-28 -- two kits worth, and probably at CR1 -- at the recommended 1.5V voltage.
I also discovered a G.SKILL forum post, members exchanging with one of their tech-reps. He seemed to think you could run them at 9-10-9-28 by upping the voltage to 1.65V.
Generally there will be a trade-off between timings, voltage and speed. Want more speed? You may increase the voltage to keep the tighter timings and increase the speed. Or you can loosen the timings, keep the same voltage, and increase the speed. This might also work in reverse -- if you want tighter timings, you either need lower speed or higher voltage.
You also have a choice when you're still shopping for RAM. You can either buy good RAM rated at a lower speed and tighter timings -- to find that they're scalable at the same timings to higher speed well within the warranty voltage limit. Or -- you could choose to buy more expensive RAM spec'd at a higher speed, knowing that you may want to run them at a lower speed, lower voltage, and/or tighter timings.
To get a handle on how you might choose timings for test purposes that depart from the spec, review a tutorial on latencies and the relationship between them. Otherwise, gather "intelligence" such as I've provided here as example.
Incidentally, with the Sabertooth Z77, you may want to focus your attention on the VCCIO and VccSA settings. I'm only guessing that the Z77 chipset and BIOS on the Sabertooth provide a manual adjustment for VccSA, but it's likely not necessary. There is enough advice extant that says you can or should leave VccSA alone. It's the voltage for the integrated memory controller itself, and supposedly the controller is strong enough to handle a range of speeds and timings.
From my tests in my Z68 ASUS board with HCI Memtest so far, I'm pretty sure you can get those modules to run at 1866 as I explained -- probably by edging VCCIO up to 1.1 or less than 1.2V. Actually, 1.1 is default or "recommended." the "safe" limit on VCCIO is probably about 1.35V. Conventional wisdom says keep it between 1.1 and 1.2.
I say this because I'm still "testing," and I got 4x4GB of the GBRL's to run at that speed 1866 through 380% coverage with HCI Memtest before the first error (after OMG! 20 hours). My VCCIO was set at 1.076; RAM voltage was about 1.51V. I was tweaking the VCCIO from a failure at 7%, then at 49%, and finally (so far) 380%. So, 1000% coverage without failure is . . . near at hand . . . . very close . . .