I am Australian, and for no one real reason, don't drink that much at all any more, mostly for convenience of being able to drive for dropping off and picking up children etc.
But, as a country, drinking is historically Australia's national past time, and we used to eclipse all others including the Germans, but trailing off a bit these days, I think.
But, based on personal experience and empirical observations, a six pack a night, of American beer, most people in Australia would class that as necessary rehydration, maybe undertaken before breakfast.
If it was, say, two bottles of wine a night, I'd be saying that I have seen that sort of level to potentially have a detrimental effect, but in many ways other than cognitive before that would creep in.
You also have to take into account that your body will become to a certain extent accustomed to alcholo use and you tend to build up tolerance via production of more enzymes to break alcohol down, shaping of your drinking habits (eg guzzling vs drinking) type of alcohol you choose and so on.
I do not advocate use of alcohol in an extensive or pervasive way, and statistically alcohol is one of the worst drugs there is, partly because of availability. But I feel there are worse things that you can be doing to yourself, including excessively stressing out about things, like work, or drinking too much...
There are many things you can do to start to minimise impacts.
For instance if you start to not really know how many drinks you have had, put the bottle top or ring pull in your top pocket for each drink, measuring something is the first step to controlling something.
Also, it is not just the amount you drink, it is the rate you drink and the condition of your stomach when you drink that makes a big difference.
Rule of thumb is for an adult male it is 0.01 BAC ( 0.01g of alcohol in every 100ml of blood. ) out, or processed every hour by the body. (YMMSV)
And one standard drink is 0.01 BAC in. One can American standard beer is about 1 standard drink, strong beer maybe up to 2.
If you space out your beers, say by having a glass of water between each one, the peak alcohol BAC can be substantially reduced, it's basic queueing theory. Plus the impact of any dehydration will be greatly diminished and the next morning should be somewhat more pleasant.
And make sure to have some food first, the rate of absorption on an empty stomach can be substantially greater than one that has food to dilute the alcohol in the stomach.
But, regardless of all this, if you start having episodes where you can’t remember, or maybe act inappropriately, causing regrets, it is wise to seek some help if you cannot diminish these effects on your own.