i have an echlin gx80 "performance" coil, it's served me well, nice fat blue sparks. stewart runs these with jaycar HEI and pulls about 8 amps thru them, even with that punishment, they usually last a couple of years before they die
surprisingly, i found a cheap efiparts.com coil was more powerful than my echlin, and about 10 or 20 dollars cheaper. i was getting all these thru aussie auto stores (there's one of them at the turnoff to shailer park, the hyperdome or whatever it's called)
if i was going to upgrade, i'd go to an electronic ignition coil (not a cylinder thing, kindof like a little block), or just bite the bullet and get a full MSD setup