PHP 7.2.7 (cli) (built: Jun 19 2018 23:13:48) ( NTS MSVC15 (Visual C++ 2017) x64 )

## bench.php
<?php error_reporting(E_ALL);

function test() {}

$nIter = 1000000;
$argNums = [0, 1, 2, 3, 4, 5, 100];

$func = 'test';

foreach ($argNums as $argNum) {
    $args = $argNum == 0 ? [] : array_fill(0, $argNum, null);

    $startTime = microtime(true);
    for ($i = 0; $i < $nIter; ++$i) {
        call_user_func_array($func, $args);
    }
    $endTime = microtime(true);
    echo "cufa   with $argNum args took ", $endTime - $startTime, "\n";

    $startTime = microtime(true);
    for ($i = 0; $i < $nIter; ++$i) {
        switch (count($args)) {
            case 0: $func(); break;
            case 1: $func($args[0]); break;
            case 2: $func($args[0], $args[1]); break;
            case 3: $func($args[0], $args[1], $args[2]); break;
            case 4: $func($args[0], $args[1], $args[2], $args[3]); break;
            case 5: $func($args[0], $args[1], $args[2], $args[3], $args[4]); break;
            default: call_user_func_array($func, $args); break;
        }
    }
    $endTime = microtime(true);
    echo "switch with $argNum args took ", $endTime - $startTime, "\n";

    $startTime = microtime(true);
    for ($i = 0; $i < $nIter; ++$i) {
        $func(...$args);
    }
    $endTime = microtime(true);
    echo "unpack with $argNum args took ", $endTime - $startTime, "\n";
}

## results
// RUN 1:
cufa   with 0 args took 0.43453288078308
switch with 0 args took 0.24134302139282
unpack with 0 args took 0.12418699264526
cufa   with 1 args took 0.52508997917175
switch with 1 args took 0.27617788314819
unpack with 1 args took 0.1316659450531
cufa   with 2 args took 0.5653350353241
switch with 2 args took 0.37865686416626
unpack with 2 args took 0.15234017372131
cufa   with 3 args took 0.61699819564819
switch with 3 args took 0.39212608337402
unpack with 3 args took 0.15739798545837
cufa   with 4 args took 0.66614294052124
switch with 4 args took 0.44650483131409
unpack with 4 args took 0.17123508453369
cufa   with 5 args took 0.73408579826355
switch with 5 args took 0.49595499038696
unpack with 5 args took 0.18640494346619
cufa   with 100 args took 5.0327250957489
switch with 100 args took 5.291127204895
unpack with 100 args took 1.2362589836121

// RUN 2:
cufa   with 0 args took 0.43715286254883
switch with 0 args took 0.23759603500366
unpack with 0 args took 0.12323498725891
cufa   with 1 args took 0.52805018424988
switch with 1 args took 0.28081107139587
unpack with 1 args took 0.14142084121704
cufa   with 2 args took 0.58326005935669
switch with 2 args took 0.37855386734009
unpack with 2 args took 0.14764094352722
cufa   with 3 args took 0.63784694671631
switch with 3 args took 0.40486693382263
unpack with 3 args took 0.16130805015564
cufa   with 4 args took 0.67221808433533
switch with 4 args took 0.45406103134155
unpack with 4 args took 0.16867184638977
cufa   with 5 args took 0.71207308769226
switch with 5 args took 0.49642992019653
unpack with 5 args took 0.18695878982544
cufa   with 100 args took 5.0643861293793
switch with 100 args took 5.3053078651428
unpack with 100 args took 1.1865899562836

// RUN 3:
cufa   with 0 args took 0.44004893302917
switch with 0 args took 0.24612522125244
unpack with 0 args took 0.1329391002655
cufa   with 1 args took 0.54023694992065
switch with 1 args took 0.28621506690979
unpack with 1 args took 0.133131980896
cufa   with 2 args took 0.59014391899109
switch with 2 args took 0.38013100624084
unpack with 2 args took 0.14762496948242
cufa   with 3 args took 0.62308812141418
switch with 3 args took 0.39890003204346
unpack with 3 args took 0.16549801826477
cufa   with 4 args took 0.65626192092896
switch with 4 args took 0.45355796813965
unpack with 4 args took 0.17756295204163
cufa   with 5 args took 0.72181010246277
switch with 5 args took 0.51895904541016
unpack with 5 args took 0.19365406036377
cufa   with 100 args took 5.0851991176605
switch with 100 args took 5.5029859542847
unpack with 100 args took 1.2169179916382