Just for the sake of TIMTOWTDI:

$max = ($x,$y)[$x<$y];
$min = ($x,$y)[$x>$y];
[download]

which is a golfed version of your 2^nd variant: (sort-of) a one-step sort which eliminates building a code block frame and the call of sort. Ternary is cheaper, since it doesn't involve bulding a list.

update:
I've been working at a place where restrictive coding standards prohibited ternary and forced me to write

if ($x < $y ) {
    $max = $y;
}
else {
    $max = $x;
}
[download]

- which is as cheap as ternary (I guess) but looks convoluted to me - among other hilarities. Good riddance.