With good aftermarket cooling the Winchester core will be able to handle 1.9 vcore, although it'd be getting pretty toasty at that point.
DIMM voltage can easily hit 2.9v no problems as mentioned, one of the common problems with motherboards is actually the limit the DIMM voltage can be pumped up. Many people need 3+ DIMM voltage.
People who need +3 dimm voltage are only those with BH-5 chips for the most part. That $108 gig kit of TwinMOS is 'valueRAM' but it can hit some nice OC's with like 3.2v and higher....but if you're using TCCD's you really don't need higher voltages, although I have seen some people get really tight timings with higher voltage on the TCCDs.
That geil ram is horrible, I can't believe those insanely loose timings, you MIGHT be able to tighten them up if you boost it up to 2.9 dimm but that's not guarantee
Winchester as been said can take a fair amount of voltage but you really need to keep it cool. I don't think I've seen too many people putting 1.9v through them though because generally they reach their limit long before you even get up to that high of voltage