Is it officially accepted by most police districts that the left most lane is for faster driving? How much faster are you usually allowed? It seems like they would condemn any sort of speeding (past a certain tolerance), no matter what lane it occurs in. On my commute, the speed limit’s 55, but traffic does 70ish. As this is already above the limit, would 75 be fine in the fast lane? 80? I know it’s generally officer’s discretion, but are there baslines?
kinda. Back when I worked at the bank, we had quite a few police officers come in. I took advantage of my position of power to be slow and delay them to ask them questions such as how fast someone has to be going to be pulled over. Seems common consensus is that 13 over is the magic number everywhere. 13 over in town, 13 over on the freeway, it’s the same to them.
But then again, this comes from what only 11 cops told me, and only 3 of them state troopers that actually patrol the freeways. And I had one say 5 over. Scary, eh?
I would’t have any confidence in my safety from speeding tickets the second I go even a little over the posted limit. They can haul you over for going 1 over the limit, and even if they can’t or don’t make it stick, you still get pulled over and put through the whole process… which is what you want to avoid. True, they generally allow you a bit faster and acknowledge the fast lanes, but it’s all up to their own discretion. Some will follow the same guidelines, others don’t… and they don’t wear nametags teling you which they prefer. I’ve known far too many people who assume cops always allow you X over the limit, and they go to the trouble of figuring out how much over in different places at diff times during the day, you know, really make a science of “exceptions to the rules”. Trouble is it’s all there, but not there. If a cop or trooper hasn’t met his quota for the day/week, he can throw your whole term paper out the window and you’re stuck with a ticket that seems unfair to you, but which you really do deserve - hey, the limit’s posted. Bend the rules at your own risk.
Which is not to say that you can speed in the left-hand lane–merely that, if everyone else is driving at the legal speed limit, and you wish to drive at less than the legal speed limit, you should get over to the right. But to exceed the legal speed limit–well, that would be wrong.
Note that in MEBuckner’s reference, the active phrase is “any vehicle proceeding at less than the normal speed of traffic at the time and place and under the conditions then existing.” There is no mention of a speed limit, at all.
Similar laws are found in quite a few states and are generally known as “slow traffic keep right” laws. If slow traffic is staying to the right, then the left lane is the default “fast” lane–even if the “slow” right lane is averaging 73 and the left lane is averaging 78.
Another aspect to this situation is that several states have laws forbidding anyone from passing to the right. This means that where those laws are rigorously enforced, some jerk can do 1/4 mph over the speed limit in the left lane and bottleneck traffic for miles.
(I do not know how many states rigorously enforce such a law, but I remember a story many years ago about a New Hampshire governor having his driver do 55 in the left lane, so at one time it was enforced in that state. Whether such enforcement has continued in any state through the 90s and Aughts I don’t know.)
The left lane is the fast lane only in that the right lane is the slow lane. You still cannot exceed the speed limit (that’s why it’s called a limit), but as said before, if you’re going slower than everyone else, you should be in the far right lane. Naturally this never seems to happen. California Vehicle Code has a similar wording to that in the Georgia code stated before. Note that there is no mention of a “Fast lane” - I think that’s just a common simplification or even misunderstanding. If you’ve got a 4 lane highway, ideally (from a “legal” point of view) if the speed limit is 55, the average driving speed would be, from left to right:
55 | 55 | 55 | something less
Sometimes I look at the signs which say “slower traffic keep right” and try to justify to myself that this means if there’s a car to my right, I HAVE to go faster than him! So it’s not my fault if he’s doing 100 and I have to do 101. I don’t think this will work on the cops though! 
In Kentucky, the law is to keep in the right lane, except to pass. You can actually get pulled over(I saw it happen once), for staying in the left lane when you had the opportunity to get over. Of course, this only happens on sparsly populated highways. It’s not gonna happen on I-75.
I know that here in Oklahoma (Tulsa especially), although drivers are suppose to stay in the left lane if they are slower, motorists totally disregard this. People drive in whatever lane they please here, and go as fast as they feel like. It is very frusterating to get behind someone going 50 in the right lane and even though you came up on them going 70, they seem to think you should go around them in the left lane. It also often happens that you will get 2 cars side by side going the same speed, often 10 mph under, and they dont seem to notice that there is a huge line of cars behind them that can’t pass. If anyone in Oklahoma is reading this, please, please don’t drive like the ways I have just decribed.
Sounds like you either got the right and left lanes mixed up, or you’re getting angry at people that are rightly driving in the right lane (the travel or “slow” lane).
Not every state requires slower traffic to keep to the right, and not every state prohibits passing on the right. Nonetheless, it’s obviously generally accepted that you drive on the right, pass on the left, and pull to the right for the faster vehicles. Of course, there are millions of bozos on the road who don’t accept that.
As to the OP, the limit is of course the limit–you’re taking your chances if you exceed it by one MPH, and the more you exceed it, the greater a chance you’re taking.