I know the concerns about bike thief, and 600 is a lot of money to a lot of folks. Especially to people in the more rural areas, or cities where industry has abandoned them. Thief also does seem to be a high risk for your city.

The Kryptonite New York line is pretty hefty, for both u-locks and chain types of security. The best way to be safe about parking bicycles is to never park them on the street, and take them inside with you as much as possible so you can keep an eye on it. If it is to commute, ask the building management or supervisor if there is a secure area in the garage or something to park the bike. If it is for trips to the store, I think it can be fine to lock it up outside, just don't leave alone for too long and make sure to take all your 'accessories' with you.

It is true that car jacks can defeat u-locks, and that is why you want to get the smallest one that you can use with your bike. The standard size kryptonite New york U-lock (8in by 4in) is probably good for most situations. If you can get away with using a smaller u-lock, you should get that one. If the thief can get liquid nitrogen, then I am afraid that they are well prepared to steal your bike, and you probably wouldn't be able to stop them short of seeing them in the act and calling the police. The same can be said with power tools. You also have to keep in mind the New York series is pretty heavy in itself. You can still probably get something like the series 4 evolution and still be pretty safe, as long as there are other lessor secure targets than your bike. I hate to say it but the thief will probably move on to the next bike if your's is hard to steal and they see something easier to take.

Amazon is my go-to place, because it's usually cheaper and I don't get charged tax.