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Your 3-rep weight should be a fair amount heavier than your 5-rep weight. By the third set you should be really pushing hard to get rep 3. By the 5th set i'd expect to see some failure, some dropping the bar. Try and hit your 1-rep max for a set of three. I am betting you can do it.
Go as low as you can. Ass-to-grass will make you a better athlete and will make you surprisingly stronger when you try to hit a new one=rep max at competition depth, which is hip joint below the knee joint. To reiterate - competition depth is the minimum (unless you're injured) and maximum depth is what we should be trying to hit on everything that isn't a one-rep max.