I personally do not have any experience with Diamana shafts. Historically, the fairway clubs have a heavier shaft than the driver. I prefer to use what feels better to me, yes subjective, I know, lol. My driver is 75g and I like the Rombax because it responds well to my quick transition. I had a 68g in my 5 wood (no 3 wood at the moment) and went to a heavy 86g shaft in it for last season. I already have the 68g swapped back in for this year. You don't have to follow the norm I guess, just go with whatever feels best for you and what suits your swing.
Just don't get caught up in this "All stock shafts are crap" manure that people seem to get into, because they aren't all crap. Sure, maybe the quality control might be a little more slack with mass production, but that doesn't mean there aren't some nice shafts out there that don't cost an arm and a leg. Most of which probably came in someone's off the rack golf club. Like was stated earlier, why would a company lend their name to a shoddy product, when their main income relies on those products? Club manufacturers and players are both caught up in getting more distance, and that's being answered with lighter and lighter products. Keep making things lighter with the same old technology, and guess what? Something is going to eventually break.
Then again, maybe I am just talking out of my a..