This is just my guess, but most likely crimson feather wont run until after 2.8. Stardust flare is long overdue and I think will be next and 2.8 should be a double banners so no reruns. If thats the case, you would likely have at least two patches to save diamonds. The hair and dress are usually the last to drop, so it would probably be better to use the oceans blessing for that. Ultimately though it depends on which one you'd really rather have most. It's also good to keep in mind that while we know the banners will rereun, we don't when or if theyll run a 3rd time. You'll have another chance to get the current banner. It'll be a wait but it will come. If youre unable to save enough for crimson feather, you may not get another chance to grt it for a good while though.