I always try out lubed fiber wads with a new gun because I like their benefits in my uses. Lots less fouling issue when taking lots of shots- I never have to swab, even on days involving 40 or 50 shots. They're also lots easier to handle than cards with cold fingers or gloves. Those thin "over shot" cards lots of guys like to use between shot and powder are a royal PITA when the fingers aren't working so well.
Starting from the position of someone liking them and working on load development, I have always been able to find loads that work. A good rule of thumb is that if you're getting donuts, you're using too much powder for a particular shot charge. When using 10 grains less of powder (by volume, not weight) than shot, I always manage to get good patterns. I can use equal volumes with 1f powder rather than 2f, so I lean that way most days now simply because I can use the same measure for both.
I'm convinced the deadly "donut" is due to gas escaping around the fiber wad and up into the shot column, rather than the wad blowing up through the shot at the muzzle. If a fiber wad was prone to blowing through the shot, then it would be even more likely with lighter cards.
One thing I've found universal between my shot loads: I put a 1/8" thick "Type A" hard card beneath the fiber wad. It does a good job of scraping fouling when you seat it down the bore, plus it always seems to improve a pattern. Haven't tried it yet as an "over shot" card, but fully intend to do so. I'll be happy if it doesn't improve patterns at all, so long as it doesn't make them worse. I'm just looking for a card that's easier to handle than thin cards with uncooperative fingers.
Bottom line, do lots of load testing to see what your gun likes best. "Best" for me is a nice even pattern with no ragged fringe and no clumping or "dense core" in the middle of the pattern. A turkey hunter might want that dense core, but I'm a wing shooter and not a turkey poker.
