I don't know about Saracione reels or other modern spools warping like you describe, but the cast aluminum spools in old Hardy reels can/may split or crack under the pressure.
i do not put backing on any tighter than I would normally recover it when fishing.
if it is wound on extra tight when spooling on fresh and you do actually end up well into the backing- can you wind it back on tight enough to not have an issue with line space on the river?
just my non expert thoughts
I have often considered using braid for backing but have been concerned about cutting my fingers while holding against a fast running fish? Are you controlling strictly by the reel once the backing is in play? Are there others using Braid?I run braid on a lot of my reels that are marginal for dacron capacity. I spool it on TIGHT. I weave it through my leather gloved fingers to adjust for tension and crank that stuff on.
I've used braid, where reel capacity is in question, with no problems. When a fish is into the backing/braid I use the drag, or palm the reel. I never hang on to the backing.I have often considered using braid for backing but have been concerned about cutting my fingers while holding against a fast running fish? Are you controlling strictly by the reel once the backing is in play? Are there others using Braid?