Here in NJ most of our highways are 50mph, and all the highways I use are 50mph. I choose my speed depending on the highway. On the Palisades Interstate Parkway, which I use every day to get to school and back, it is a 50mph zone and I can safely go 62mph. I have never been pulled over on this highway. I also use route 4 on a daily basis for my commute to school and back, also a 50mph zone but much more traffic, so I usually don't go faster than 58mph.
I go 30mph in 25 zones, 40mph in 35 zones, 48mph in 40 zones, and ~60mph in 50 zones. My speeds are based on roads I know I can safely exceed the speed limit on. When I am traveling on unknown roads, I usually back down my speed quite a bit. Every once in a while, to get it out of my system, I do double the speed limit of every zone (even your insurance company doesn't give you a "pat on the back" for being a good driver).
Here's a general tip: If I were pulled over for 4mph over the speed limit, I would explain to the officer that perhaps my speedometer is not properly calibrated...it's not uncommon for speedometers to be off by 3-4mph, and this gives you some "lee-way" but don't be surprised if you are pulled over for going 29mph in a 25 zone, for example. Remember that the speed limit is a speed LIMIT (not a "you can go a few mph over this speed" sign), and TECHNICALLY, this LIMIT is based on "conditions permitting". If it's raining or crappy weather, it is your duty as a driver to reduce your speed to a safe rate if necessary.
I have several speeding tickets and I can't even count how many times I've been pulled over in my short 5 years of driving, and although I hate pigs and dealing with them, I have found that as I have gotten pulled over so many times, I know how to deal with cops much better. For example, the last time I got pulled over, was because I spun my rear tires in front of one cop directing traffic and floored it in first gear up the street right to the next cop (massive traffic jam and there were cops directing traffic at every block). Got pulled over for like 10 minutes and I drove away ticket-free...didn't even get a ticket for my 15% tint after the officer pointed it out. It's all about the communication skillz....