As is indicated in the posts above, the number one thing with masts is that the sail you have fit them. Unfortunately, this can not be evaluated by just looking at IMCS numbers and such things. You have to try it out or maybe listen to somebody that has tried the particular combination out.
As for carbon masts being more sensitive, yes they can be, but it is in fact not so much the carbon itself being so much more sensitive. Th "problem" is that the stiffness of carbon is so high that you can use so little of it and still make the mast the right stiffness. Then, each single little fiber carries a bigger percentage of the load and hence any single litte damage will harm the mast more.
If you follow that logic, it is not hard to see that 100%rdm masts are actually not (necessarily) very sensitive since here you use a smaller diameter to lessen stiffness and hence be able to add more material. There are 90-100% carbon rdm that are stronger than ANY sdm and also less sensitive to mistreatment off water.
But just as with sdms, when if you try to make an rdm super light (ie go significantly lower than say 1.5kg for a 4m mast) you will again approach the limit were the mast will become sensitive and not very strong.
Its not only the weight though. Designing and constructing a mast is very difficult. Also seemingly very similar mast can be very different when it comes to strength. Its all about eliminating weak spots.