Benchmarking is very hard because even the same language could show different results. For example: for($i = 0; $i vs $count = count($list); for($i = 0; $i Most of the time benchmarks prove how capable a programmer is, not the speed of the language used.
Any decent compile-time optimizer will transform your first snippet into the second one (or better). Some languages preclude that optimization at compile time, but I presume that a JIT would also have little problem performing that optimization. That is, one could argue that a good language is one that lets developers ignore trivial changes like this without hurting performance.
More as a reference for others, this is a fun page that highlights a few interesting optimizations GCC 4.2 is capable of making: http://ridiculousfish.com/blog/posts/will-it-optimize.html Maybe the optimizer can deduce guarantees about a function, but the writers may have just included an optimization for a specific built-in because the unoptimized form is such a common mistake...