Very unscientific benchmark of PHP 5.4 traits against Silverstripe Extensions at mixed-in function calls. Results on my late 2011 MBP: Traits are between 10 and 40 times faster.

gistfile1.txt

<?php
/**
Results on my Macbook:
Native function (no Object, no traits): 0.12234592
Native function (no Object, traits): 0.13018894
Native function (traits): 0.15913486
Native function (extension): 0.12871218
Mixin function (traits): 0.12146902
Mixin function (extension): 4.077214
Random functions (traits): 0.46887112
Random functions (extensions): 4.22944283
**/

class timer {
	var $start;
	var $pause_time;

	/*  start the timer  */
	function __construct($start = 0) {
		if($start) { $this->start(); }
	}

	/*  start the timer  */
	function start() {
		$this->start = $this->get_time();
		$this->pause_time = 0;
	}

	/*  pause the timer  */
	function pause() {
		$this->pause_time = $this->get_time();
	}

	/*  unpause the timer  */
	function unpause() {
		$this->start += ($this->get_time() - $this->pause_time);
		$this->pause_time = 0;
	}

	/*  get the current timer value  */
	function get($decimals = 8) {
		return round(($this->get_time() - $this->start),$decimals);
	}

	/*  format the time in seconds  */
	function get_time() {
		list($usec,$sec) = explode(' ', microtime());
		return ((float)$usec + (float)$sec);
	}
}


class A extends ViewableData {
	use tC, tD, tE, tF, tG, tH;
	public $count = 0;
	function f1() { return $this->count++; }
}

class AA {
	use tC, tD, tE, tF, tG, tH;
	public $count = 0;
	function f1() { return $this->count++; }
}

class AAA {
	public $count = 0;
	function f1() { return $this->count++; }
}

class B extends ViewableData {
	private static $extensions = array('C','D','E','F','G','H');
	public $count = 0;
	function f1() { return $this->count++; }
}

class C extends Extension {
	public function f2() { return $this->owner->count++; }
}
class D extends Extension {
	public function f3() { return $this->owner->count++; }
}
class E extends Extension {
	public function f4() { return $this->owner->count++; }
}
class F extends Extension {
	public function f5() { return $this->owner->count++; }
}
class G extends Extension {
	public function f6() { return $this->owner->count++; }
}
class H extends Extension {
	public function f7() { return $this->owner->count++; }
}

trait tC {
	function f2() { return $this->count++; }
}
trait tD {
	function f3() { return $this->count++; }
}
trait tE {
	function f4() { return $this->count++; }
}
trait tF {
	function f5() { return $this->count++; }
}
trait tG {
	function f6() { return $this->count++; }
}
trait tH {
	function f7() { return $this->count++; }
}


class MyBenchmarks extends Controller
{
	private static $allowed_actions = ['index'];

	function index() {
		echo "Running some crazy benchmarks:<br>\n";
		$t = new timer();
		$numRuns = 1000000;

		$t->start();
		$obj = new AAA;
		for ($i = 0; $i < $numRuns; $i++) $obj->f1();
		echo "Native function (no Object, no traits): " . $t->get() . "<br>\n";

		$t->start();
		$obj = new AA;
		for ($i = 0; $i < $numRuns; $i++) $obj->f1();
		echo "Native function (no Object, traits): " . $t->get() . "<br>\n";

		$t->start();
		$obj = new A;
		for ($i = 0; $i < $numRuns; $i++) $obj->f1();
		echo "Native function (traits): " . $t->get() . "<br>\n";

		$t->start();
		$obj = new B;
		for ($i = 0; $i < $numRuns; $i++) $obj->f1();
		echo "Native function (extension): " . $t->get() . "<br>\n";

		$t->start();
		$obj = new A;
		for ($i = 0; $i < $numRuns; $i++) $obj->f3();
		echo "Mixin function (traits): " . $t->get() . "<br>\n";

		$t->start();
		$obj = new B;
		for ($i = 0; $i < $numRuns; $i++) $obj->f3();
		echo "Mixin function (extension): " . $t->get() . "<br>\n";

		$t->start();
		$obj = new A;
		for ($i = 0; $i < $numRuns; $i++) {
			$fn = 'f' . rand(1, 7);
			$obj->$fn();
		}
		echo "Random functions (traits): " . $t->get() . "<br>\n";

		$t->start();
		$obj = new B;
		for ($i = 0; $i < $numRuns; $i++) {
			$fn = 'f' . rand(1, 7);
			$obj->$fn();
		}
		echo "Random functions (extensions): " . $t->get() . "<br>\n";
	}
}