The rule for average types of nonbottle-conditioned beers is to get em in the fridge and drink em as soon as possible because for certain, nothing good will happen to the beer by hanging on to it. The exceptions to this rule are with bottle-conditioned beers and some high alcohol beers. Obviously, with bottle-conditioned beers, the beer must carbonate in the bottle and this takes time. Meaning the beer improves for some time and then begins its downhill slide.
Some high alcohol beers improve with age and much of the improvement with these beers is actually a product of oxidation. Many aged big beers, such as barleywines, take on flavors reminiscent of sherry (that also gets much of its flavor from oxidation). I know of no rule of thumb matching the alcohol content of beer with its ability to age gracefully. I typically try to imagine how a beer would taste if it was rounded out by age. Many strong beers that do seem to benefit from age are big, malty and balanced by assertive hop bitterness when young. I think this is why many strong ales seem to improve with age. I myself have Belgian Strongs and Chocolate Stouts rounding 4 years.
The only reliable way to monitor a beer and determine when it reaches its peak is to taste it. This requires a whole bunch of the same beer and persistent quality control. Meaning you have to drink your stash and take notes on its progress. Ideally you will note the point when the beer is ever so slightly passed its peak and you can finish off the remainder before the flavor really begins to suffer. You may see a trend with beers under 6% normally hitting their peak between 3 to 6 months. Times may vary depending on cellaring practices.
Hope that helps,
Wild