Taking out the capturing parenthesis around the whitespace helped a lot. Here's the benchmark results:

Benchmark: timing 50000 iterations of regex, split...
regex:  3 wallclock secs ( 3.03 usr +  0.01 sys =  3.04 CPU)
split:  4 wallclock secs ( 3.79 usr +  0.00 sys =  3.79 CPU)
[download]