The thing is that if somebody is 225 at 5'8" and under 8% bodyfat, they are certainly way past their genetic limit, and probably blast and cruising to maintain it.
Genetic potential is a hard thing to judge and accurately give an example of, because it is so individually specific..but if you are 6 foot, in single digit bodyfat, and 220 lbs you have to at least figure you are damn close to it if you haven't met it yet. If you come off of a cycle and seem to lose more than normal and continuously end up back at the same weight over time...it may be a good indication you are at genetic potential. The only way to get past it at that point is to never come off (blast and cruise)