A bit faster, maybe. Stop making it evaluate $lines(C:\IcyBot2\gazillion.txt) all the time.
alias hunderedthousand {
var %looplength = $lines(C:\IcyBot2\gazillion.txt)
while (100000 > %looplength ) { /write C:\IcyBot2\gazillion.txt $calc($lines(C:\IcyBot2\gazillion.txt) + 1) }
}
However, reading and writing to a hard disk is always the slowest part of a program. The problem is compounded because Mirc is fairly slow to begin with.
I doubt you'll be able to do what you want within a decent timeframe.
In order to clock something just assign a variable to $ticks when the scripts starts, again when its done. Subtract the two and that's how many MILLIseconds it took to do.
var %time = $ticks
var %i = 1
While %i < 100000 { Inc %i }
/echo -a $calc($ticks - %time)
Adjust as you see fit.
Blast, I totally forgot about $fread and its ilk. See below for a much better version. (I blame lack of sleep for this entirely.)