ON3P's wood guru Caveman drops some serious knowledge on the matter in
this thread.
And no, Jeffreys are not all that heavy anymore - if not light either, more like just right imho. Sure, they have a bit of heft to them (which is good and makes them ski better, especially in variable/tracked out snow), but they are actually lighter than some comparable skis like Revolt121s and Black Ops Gamers. Jeff118s will still not feel
that heavy as the main part of the weight is closer to center, especially at speed where their shape makes them loose and fun.
As for the difference, the flex pattern will be pretty much the same, while the damp ride and ability to smash through stuff will be marginally lessened. They will still ski great. If the idea is just to save weight then you are def looking at the right segment to get this layup - a pow ski. I've gotten some 50/50 wood102s and 110s this year, but have yet to take delivery of them. I got them as travel skis, to be used mainly in resort, but to be able to tour as well. I have zero concerns that they will not hold up for me, but I am a lighter guy. Iggy has also mentioned that some ON3P empoyees get 50/50 skis to save a bit of weight for their resort skis.
My 2cents: If you are at all concerned about durability - go with the stock layup. They are about as duarable a ski as money can buy you and can take rediculous amounts of abuse as a pow ski. A 50/50 core will save you something like 200gr or some such a ski, depending on what lenght you are planning on getting - but what is the point if you are going to ski them timidly? I would 100% get the standard layup for a resort exclusive ski though - that layup just skis so well and can take soooo much abuse.