Benchmark: timing 200 iterations of lookahead1, lookahead3, lookahead4, lookahead5, nolookahead...
lookahead1:  3 wallclock secs ( 2.93 usr +  0.00 sys =  2.93 CPU) @ 68.26/s (n=200)
lookahead3:  2 wallclock secs ( 2.23 usr +  0.00 sys =  2.23 CPU) @ 89.69/s (n=200)
lookahead4:  2 wallclock secs ( 2.03 usr +  0.00 sys =  2.03 CPU) @ 98.52/s (n=200)
lookahead5:  2 wallclock secs ( 2.00 usr +  0.00 sys =  2.00 CPU) @ 100.00/s (n=200)
nolookahead:  7 wallclock secs ( 6.30 usr +  0.00 sys =  6.30 CPU) @ 31.75/s (n=200)