Yes, tires do harden with age, eventually cracking. When BFG first came out with the T/A, they raced them. For racing they shaved the tread down to make the tread blocks more stable. It would be the same for wearing them down 50%.
I run 235/60-15 T/As all around on my Demon. Just for grins, I looked over at tirerack.com and found that I had four choices in my size, Pirelli 6000, BFG T/A, Firestone Firehawk 500, Goodyear Eagle GT II. I knocked off the Pirelli @ $211 per tire as being too expensive. The GT II had a narrower treadwith, so I knocked it out of further investigation. Most telling for me was that more Firehawk owners would buy the same tire again than would T/A owners.
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