More than theoretical. I got it down to reliable 1 microsecond and the occasional 0 microseconds on a dual Xeon 3.06 with HT. 
#!/usr/bin/perl
use Time::HiRes qw(gettimeofday);

my @timings = (0,0,0,0);
#discard once
@timings = (gettimeofday(), gettimeofday());

@timings = (gettimeofday(), gettimeofday());
print "$timings[0]$timings[1]\n";
print "$timings[2]$timings[3]\n";

__OUTPUT__
1133364015468783
1133364015468783

[download]
So the answer to the OP is yes - you *can* get identical timestamps out of Time::HiRes with a sufficiently fast system.

In reply to Re^2: OT How fast a cpu to overwhelm Time::HiRes by Anonymous Monk
in thread OT How fast a cpu to overwhelm Time::HiRes by zentara

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