I have the definitive answer. Well, it’s definitive for me: that the vast majority of syrah grown in California is too ripe to age and develop in the kind of way you see from Hermitage or Cornas. That is not a criticism of California wines, just an opinion (supported by experience) that to achieve the levels of complexity and interest which great old Rhone wines can achieve requires growing conditions that are closer to the edge of viability than we typically see here in California in most growing regions in most vintages.
There are a few exceptions, of course, but they are rare. I can count the ones I personally know about on one hand: a couple of vintages of Peay Syrahs (2005 in particular); 98 and 2011 vintages of Lagier Meredith (maybe, time will tell). I think the Rhys syrahs in some vintages have a good shot at achieving this status, but it’s early days to judge. Maybe a few post-2006 Copain syrahs in certain vintages, maybe Halcon in certain vintages and with more vine age.
A lot of people will stomp their feet and throw in ESJ, Qupe, a few others. I just haven’t seen it in any of those wines, having sampled many of them from many vintages at many time points along their aging curves (again, I’m not saying they are not excellent wines, just that IMO they will never arrive at a place similar to what some old Chave, Clape, Jamet, Verset, etc. can get to). One I haven’t tried in quite a few years is the old Que Syrah vineyard, under the Failla-Jordan then Failla labels. Would be interesting to have a few of those put away for the long term (I drank mine already, because I wasn’t sure if they had the stuffing to go the distance).
I do buy some California Syrah, but I buy it for its inherent qualities, the tastiness of the wines more at younger ages. I have Dehlinger (since you mention it) going back to 94 vintage, have drunk numerous bottles of 94, 96, 97 over the years, and while I think those wines can be tremendous, I don’t know if any of them will get to where you hope they will be.
It’s a really interesting subject, but as of right now I don’t think there are ANY aged California syrahs that can “compete” with Rhones at comparable ages.