Kryptonite are plenty strong, they are a good deterent, but not theft proof by any means. I've talked with people who's job was to cut bike locks. It was generally something like cables, 15 seconds. Offbrand u-locks 45 seconds and 1/3rd of a cutting wheel, name brands minute in a half and a cutting wheel. Then the "new york style" heavy ulocks were on the order of 5 minutes and 3 wheels.
Certainly there are bigger cutting discs, if you are willing to make a bunch of noise and sparks you can cut them more quickly.
Sorry to hear that. It's the strongest lock I've come across[0], but yea, once power tools come into play I can't imagine much of anything standing up to metal cut off grinder. What do you use now to secure your ride?
[0] http://www.kryptonitelock.com/content/kryt-us/en/products/pr...
Don't. My bike was stolen by rapidly sawing (dremeling?) through a Kryptolok in broad daylight in a place with some of the most heavy law enforcement presence in Europe. Their locks are much weaker than their marketing.