IMO how you feel when lifting has a lot to do with the level of your health overall. Like some said - nutrition, hydration, etc. have much to do with what weights you are hitting...then again some people just 'have it' no matter what. For the rest of us - finding out what works best for us takes time.
Time is needed to develop the muscles for the required lifts, since that is what we train for in powerlifting. I used to weigh 150 at 10% bodyfat and was strong in many forms of lifts, but I could only squat 315 one time at my 'heaviest'. Now I have squatted 315 off a low box at 135 and I have no idea what my bodyfat is...probably somewhere around 17%. Not being too lean probably protects our tendons, joints and etc. from possible tears, etc., but the top level PL's I have watched lift - many are not fat.
If you want to compete in a certain weight class I think it is best to stay somewhere around that within 8-10lbs if you can. That way when the time comes to weigh in - you don't have to put your body through such stresses where it won't perform under optimal conditions as it normally would.
In the end, I think many achievements come from a combination of fitness level, training knowledge, nutrition and a knowledge of our own body - developed over time with trial and error. I don't feel these achievements can be attributed to just the gain or loss of bodyfat alone. Just my .02.
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Mythicwrld
"We deceive ourselves when we fancy that only weakness needs support. Strength needs it far more."