I finally got off my lazy back and ran the test on my home machine, a trusty P-100 with 80 MB RAM, and here are the results (with ActivePerl 5.005_03 build 517):

t1: 17 wallclock secs ( 6.66 usr +  9.89 sys = 16.55 CPU)
t2: 16 wallclock secs ( 5.89 usr +  8.47 sys = 14.36 CPU)
t3: 41 wallclock secs (16.67 usr + 18.16 sys = 34.83 CPU)
t4: 27 wallclock secs ( 8.37 usr + 16.88 sys = 25.26 CPU)
t5: 15 wallclock secs ( 7.75 usr +  7.07 sys = 14.82 CPU)

t1: 96 wallclock secs (30.07 usr + 59.09 sys = 89.17 CPU)
t2: 87 wallclock secs (27.73 usr + 53.18 sys = 80.91 CPU)
t3: 179 wallclock secs (72.02 usr + 96.92 sys = 168.94 CPU)
t4: 142 wallclock secs (36.63 usr + 96.15 sys = 132.78 CPU)
t5: 81 wallclock secs (35.33 usr + 43.25 sys = 78.58 CPU)

So here File::Find is again on par with the solution reading any directory twice and the solution using rewinddir(), and my favourite method of doing stuff, &t4 dosen't look that good either if you are going for peak performance. The fastest solution takes only half the time, and scanning the whole NTFS HD did take some time as you see :). So once again the rule number one of optimizing holds. Benchmark, benchmark, benchmark.